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This publication is no longer validPlease see http://www.ns-iaea.org/standards/SAFETY SERIES No.2 5Medical SupervisionofRadiation WorkersWHOJOINT PUBLICATION ($8%ILOINTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, <strong>1968</strong>


This publication is no longer validPlease see http://www.ns-iaea.org/standards/


This publication is no longer validPlease see http://www.ns-iaea.org/standards/MEDICAL SUPERVISIONOF RADIATION WORKERS


This publication is no longer validPlease see http://www.ns-iaea.org/standards/Printed by the IAEA in AustriaJune <strong>1968</strong>


This publication is no longer validPlease see http://www.ns-iaea.org/standards/SAFETY SERIES No. 25MEDICAL SUPERVISIONOF RADIATION WORKERSIN T E R N A T IO N A L A T O M IC E N E R G Y A G E N C YV IE N N A , <strong>1968</strong>


This publication is no longer validPlease see http://www.ns-iaea.org/standards/M EDICAL SUPERVISION OF-RADIATION WORKERS(S a fe ty S eries, N °25)A B ST R A C T , A revised ed itio n o f S a fe ty S erie s N °3 , " S a fe H andling o f R ad io iso to p es:M ed ica l A ddendum ". It was prepared at the request o f the IAEA, ILO and WHO by Dr. H. Ja m m e t,(S a c la y N u clear Research C en tre, F ran ce) and Dr. F. H er£ik (In stitu te o f Biophysics, C zech o slo v akA cad em y o f S c ie n c e s, Brno), who had co llaborated in w riting the orig in al e d itio n . T h e book providesinform ation necessary for im p lem en tin g th e controls in the m ain m anual (S a fe ty S eries No. 1)and an introduction to te ch n ic a l problem s of ra d io lo g ical protection.C ontents: Introd uction; 1 - B asic co n cep ts; 2 - R ad io lo g ical hazards; 3 - R adiation protec tio n standards; 4 - H ealth supervision; R eferen ces and Bibliography.A v a ila b le sep arately in English and French.(1 1 8 p p ., 1 4 .8 x 21 c m ,'p a p e r-b o u n d , 19 figures; 19.68) • • P rice: U S $ 3 , 5 0 ; £ 1 . 9 .2THIS GUIDE IS ALSO PUBLISHED IN FRENCHMEDICAL SUPERVISION OF RADIATION WORKERSIAEA, VIENNA, <strong>1968</strong> ■' • -STI/PUB/201


This publication is no longer validPlease see http://www.ns-iaea.org/standards/FOREWORDIn 1960 the <strong>International</strong> <strong>Atomic</strong> <strong>Energy</strong> Agency published amanual, No. 3 in its <strong>Safety</strong> <strong>Series</strong>, entitled "Safe Handling of Radioisotopes:Medical Addendum". It contained information necessaryto medical officers concerned with the implementation of the controlsgiven in the original manual, "Safe Handling of Radioisotopes",<strong>Safety</strong> <strong>Series</strong> No. 1. To bring the Medical Addendum up to date, the<strong>International</strong> <strong>Atomic</strong> <strong>Energy</strong> Agency, the <strong>International</strong> Labour Officeand the World Health Organization decided that a revised editionshould be prepared as a joint project and that its scope should beexpanded so that it would become a more complete guide — a separatedocument rather than an addendum to another publication. However,it was felt that, to keep the document to a reasonable size, its subjectmatter should be restricted to the medical supervision of the radiationworker under normal working conditions, that is, accident situationsshould be excluded.The three organizations asked Dr.H. Jammet (Saclay NuclearResearch Centre, France) and the late D r.F . HerCik (Institute ofBiophysics, Czechoslovak Academy of Sciences, Brno), who hadcollaborated in writing the original edition, to undertake this revision,with the help of Drs. H. T. Daw (IAEA), J. V. Nehemias (ILO)and H. Parker (WHO). The views expressed are those of the authorsand do not necessarily represent the decisions, the scientific opinionor the stated policy of the three co-sponsoring organizations.


This publication is no longer validPlease see http://www.ns-iaea.org/standards/CONTENTSINTRODUCTION ...................................................................................... 11. BASIC CONCEPTS................................................................ 31.1. Basic information on ionizing radiation.................. 31.2. Basic information about radiobiology...................... 101.3. Radiopathology............................................................... 331.4. Metabolism and toxicity of radioactive materials .. 442. RADIOLOGICAL HAZARDS ................................................ 532.1. Exposure to natural radiation..................................... 532.2. Medical exposure........................................................... 542.3. Occupational exposure ................................................. 582.4. Conclusions..................................................................... 613. RADIATION PROTECTION STANDARDS.......................... 633.1. G en era l............................................................................ 633.2. Basic standards............................................................. 673.3. Secondary standards (Derived standards)................ 734. HEALTH SUPERVISION........................................................ 834.1. Radiological m onitoring............................................... 834. 2. Medical supervision..................................................... 1004. 3. Health f ile s .... ....................................................... 114REFERENCES AND BIBLIOGRAPHY 118


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This publication is no longer validPlease see http://www.ns-iaea.org/standards/INTRODUCTIONExposure to ionizing radiation can give rise to lesions both inthe exposed individual and in his descendants, i. e. somatic lesionsand genetic lesions.With the increasing use .of ionizing radiation by man, an increasingnumber of persons incur the hazard of exposure to ionizingradiations. It is obvious, however, that man derives great benefitsfrom the use of ionizing radiations. In principle the. problem consistsof keeping the radiation dose within limits such that the risk is notexcessive either for the individual or the population as a whole. Thishas led to the notion of 'permissible dose1'. The aims of radiologicalprotection are to ensure that nobody is exposed unduly to radiation,and thus to prevent or reduce to a minimum .somatic lesions and unfavourablemodifications of hereditary genetic features.To ensure the radiological protection of workers exposed toionizing radiation, it is necessary to set up a strict system of surveillance,including both procedures for the individual physical detectionof absorbed radiation and medical supervision of,the workers'health. As m edical examination methods at present are not sufficientlysensitive to detect the effects of the low radiation doses thatcorrespond to the maximum permissible doses to which workers maybe occupationally exposed, it is sometimes concluded that medicalsupervision is only of secondary importance and may even be abandonedif there is adequate physical monitoring. In fact, however,medical supervision and physical monitoring are not only compatiblebut even complementary: physical monitoring is essential for evaluatingthe radiation doses received and preventing over-exposure,while medical examinations are necessary to follow trends in theindividual's health. The methods of surveillance needed depend onthe particular nature of the radiation hazards to which workers maybe exposed. These hazards have two main form s: exposure toexternal radiation, and internal contamination by radioactive substances.Either of them can cause irradiation of the organism andthis irradiation may occur either regularly, under normal workingconditions, or in an unforeseen manner following an accident.The first part of this volume is concerned wich the basic radiobiologicalphenomena, since understanding the problems connectedwith the medical supervision of workers exposed to ionizing radiationscalls for an adequate knowledge of their biological effects.Basic data on ionizing radiation are followed by descriptions ofradiobiological phenomena and the main radiopathological distur-1


This publication is no longer validPlease see http://www.ns-iaea.org/standards/bances. Special attention is given to essential information onmetabolism and the toxicity of radioactive substances.The second part deals with radiological exposure from varioussources and forms of irradiation - natural, medical and occupational.The third part provides data on radiological protection standards,since it is essential to determine the health standards capable ofensuring acceptable working conditions. General comments on thecriteria used in establishing the radiological protection standardsare followed by an examination of the basic standards and the practicalstandards.The fourth part deals with the health supervision of workersexposed to ionizing radiation and covers both physical and medicalcontrol. Physical control is necessary to keep track of radiologicalinjury. Its main purpose is to provide an estimate of the doses absorbedby workers due to exposure to external irradiation or toradioactive contamination. Medical control is designed to provideall necessary information on the health of workers before, duringand after employment. Special attention is given to medical recordsin view of their importance from the legal standpoint.2


This publication is no longer validPlease see http://www.ns-iaea.org/standards/1. BASIC CONCEPTS1.1. BASIC INFORMATION ON IONIZING RADIATION1.1.1. Types of ionizing radiationHuman beings are exposed to many sources of radiation. Someof them are natural, others are man-made. In this volume we areinterested in the medical aspects of ionizing radiation.1 Ionizingradiation is any radiation consisting of directly or indirectly ionizingparticles or a mixture of both. The directly ionizing particles areelectrons, protons, alpha particles etc. which transfer their kineticenergy and produce ionization by collision. The indirectly ionizingparticles are, forexample, uncharged photons of X-rays, gamma raysor neutrons. They are able to liberate directly ionizing electrons(X- and gamma rays) or can initiate a nuclear transformation (neutrons).X-rays are electromagnetic radiations produced by retardationof accelerated electrons in the anode of an X-ray tube. The energyof their photons and, therefore, their penetrating power depends onthe voltage (kV) applied to the tube. Increasing voltage increasesthe penetrating power and the energy of the photons (expressed inkeV or MeV). To high-energy photons correspond X -rays of veryshort wave length. This dependence is illustrated in Fig. 1, wherethe different electromagnetic radiations are shown according to wavelength.Gamma rays are electromagnetic radiations emitted by radioactivenuclides. Gamma and X-ray energy is dissipated through theinteraction of the photons with the matter in which they are absorbed.During these processes high-speed electrons are ejected to a considerabledepth in tissue. These electrons collide with atoms in theabsorbing matter and give rise to secondary electrons with low velocities.Their energy is dissipated within a short distance of the pointof origin of secondary electrons. There is no substantial differencein the action of X- and gamma rays.Neutrons are present in the atomic nuclei and are ejected fromthe atom, e .g ., in the process of fission. Neutrons have a massslightly greater than that of the proton. They carry no charge but1 Ionization is the process by which an atom or m olecule acquires either a positive or a negativecharge. Since the energy required to produce such an ion pair is 34 eV, only these radiationspossessing energy higher than 34 eV are ionizing. Light, radio, infrared aiid ultraviolet radiationsare therefore not considered here.3


This publication is no longer validPlease see http://www.ns-iaea.org/standards/ionize matter indirectly. Fast neutrons with energies between 20 keVand 10 MeV are able to set in motion nuclei of atoms with which theycollide. Protons that are very densely ionizing arise in this wayon their tracks in hydrogenous matter. Slow neutrons with energies ofup to 0. 1 eV and thermal neutrons (with energies of about 0. <strong>025</strong> eV)enter into nuclear reactions with atoms with which they collide, notonly causing indirect ionization but also producing radioactive nuclideswhich in turn induces the production of new nuclides, some whichmay be radioactive.W A V E -L E N Q T H X , X n G S T R O M U N ITSvP K>" ttw 10M 10n tt” » " 10“ 10* « ' X)7 to* 10* »* X)1 to1 10 1 10'* KT1 10‘ * 10** 10** 10'*ir J 1 _I I ' 17"60 C Y C L E S / f 10*C Y C L E S / S10»C Y C L E S la10MC Y C L E S / IE L E C T R ICVOWERC O S M IC(R A D IO . T E L E V IS IO N , R A D A R )H E A TIN O1----- 1— * 1— ---------- 1-------- 1--------r -1-------- 1--------r«r« kt* w* »■' ior7 ior‘ io"s w* io'3 w * io'' i 10 10* » * k>‘ 10* w* » 7 10' io* 10"E N E R G Y < « V )FIG. 1. The electrom agnetic spectrum [1 ],Angstrom unit - a physical unit o f length equal to 1/108 cm ; electron volt - the amount ofenergy acquired by an electron falling through a potential difference of one volt; electron voltage(V) is related to the wave-length o f radiation (X), in Angstrom units, approximately thus:V = 12 420/X ; wave-length and frequency are related By c = \ v, where c is the velocity ofelectrom agnetic waves = 3 x lO10 cm /s e c; v = frequency = cy cles/sec = vibrations per second, andX = wave-length in cm ; visible spectrum limits = 4000-8000. A, 7.5 X 1014- 3.7 X1014 cycles/sec.Alpha particles are positively charged helium nuclei emittedduring disintegration of some radioactive nuclides (e. g. polonium-210).They have a definite range in living tissue, generally less than 40m icrons. This is because of their low velocity, and as they arecharged, they produce along their path a column of dense ionization.Beta particles are electrons emitted with a continuous spectrumof energy by certain radioactive nuclides. They are also producedartificially in betatrons or in synchrotons and have a homogenousspectrum of energy. Their range in living matter is greater thanalpha particles because of their much greater speed. Generally itamounts to a few centimetres in water or living matter.4


This publication is no longer validPlease see http://www.ns-iaea.org/standards/Protons are hydrogen nuclei and therefore have a positive charge.They are produced in accelerators of different types (linear accelerator,cyclotrons, synchrocyclotrons) and may attain energies ofseveral thousands of MeV. Protons are also emitted in nuclear reactions.These protons may result from collision of the fast neutronswith hydrogen atoms in water or in other hydrogenous material.Protons produce ionization in their paths in a manner sim ilar toalpha rays. This phenomenon is used for the detection of fastneutrons.1.1.2. <strong>Energy</strong> of radiationsThe energy of radiation is expressed in electron volts (eV). Oneelectron volt is the energy equal to that gained by an electron whenit is accelerated through a potential difference of one volt. Generallymultiple units are used, e. g. one thousand eV (keV) or one millioneV (MeV).1.1.3. Interaction of radiation and matterThe main physical features of some charged-particle radiationsare summarized in Table I.When radiation passes through matter, it is reduced in intensitythrough complex interactions between the radiation and the atomsof the material traversed.Particulate ionizing radiations (alpha or beta particles) interactwith orbital electrons of the atoms and lose energy. Through thisinteraction the atom concerned is either excited (i.e . an electronis brought to a higher energy level) or ionized (i.e. the outer orbitalelectron is ejected and an ion pair is formed).Neutrons carry no charge and therefore they cannot produceionization directly. Fast neutrons collide in the body mostly withnuclei of light atoms (e.g. hydrogen). These nuclei produce ionsduring the dissipation of energy transferred from the neutron. Theslow neutrons react with matter by nuclear reactions during whichcharged particles or gamma rays are produced.The photons of electromagnetic ionizing radiations (X- and gammarays) interact also with orbital electrons and lose energy. Thereare different ways of interaction between photons and atoms. Themost common are the photoelectric effect, the Compton effect andpair production.5


This publication is no longer validPlease see http://www.ns-iaea.org/standards/TABLE I.CHARACTERISTICS OF VARIOUS RADIATIONSType Nature Source <strong>Energy</strong> PenetrationAlpha helium nuclei radioactivenuclides (zl0Po)cyclotrona few M eV up to hundredso f M eV25 pm (4 M eV) in waterBeta electrons radioactivenuclides (210RaE)betatrona few keV to several M eVup to 100 MeV1 .5 cm (Em ax 3 M eV ) inwaterProtons hydrogen nu clei cyclotron 5 - 400 M eV 8 - 23 X 104 cm in air(proton beams)


This publication is no longer validPlease see http://www.ns-iaea.org/standards/The photoelectric effect is predominant for photons of relativelylow energy (0. 01 - 0. 1 MeV), the Compton effect becomes importantin the range of 0.1 - 5 MeV and pair production occurs at energiesexceeding 1.02 MeV and predominates at 50 MeV. In Fig. 2 therelative importance of these three processes is schematicallyillustrated.EN ER GY OF PHOTONS(MeV)FIG. 2.Percentual participation o f photoelectric effect (1), Compton effect (2) and pair production(3) by absorption o f photons o f different energy [2 ].The photoelectric effect consists of the ejection of an orbitalelectron after the collision of a low-energy photon with the atom.The ejected photoelectron collides in turn with other atoms and isscattered; its track is therefore rather tortuous. When the energyof the incident photon is not sufficient to eject the electron, an excitationtakes place.In the Compton effect, the incident photon makes an inelasticcollision with a free or loosely bound.electron but loses only part ofits energy. The result of this collision is the ejection of a photoelectron.The rest of the energy of the photon travels in the formof a photon with reduced energy (and a correspondingly greater wavelength) which may again undergo Compton scattering or photoelectriceffect.When the energy of photons exceeds 1.02 MeV, a positronelectronpair may be formed. The kinetic energy of the two particlescorresponds to any energy of the photon in excess of 1. 02 MeV.7


This publication is no longer validPlease see http://www.ns-iaea.org/standards/It should be borne in mind that the above-mentioned elementaryreactions occupy a very short period of time, 10~17 - 10‘ 15 seconds.The excited or ionized atoms or molecules are very unstable andextremely reactive. As we shall see later, they undergo chemicalreactions with the formation of free, radicals or stable and unstablemolecules.It may be stated in general that, as a result of ionizing radiation,matter is permeated by electrons of various velocities andsimultaneously a considerable number of atoms are excited, i.e .become more reactive with respect to other atoms or m olecules.1.1.4. Radioactivity and radioactive decayAt the present time there are over forty radioactive elementswith high atomic weight which occur in nature. Besides that, a fewof the lighter elements, as for example potassium, rubidium andsome others, possess radioactive properties.The nuclei of radioactive nuclides as distinct from those ofinactive nuclides undergo spontaneous disintegration with the em issionof alpha, beta or gamma rays. Unstable nuclei are turned intostable nuclei after one or more such disintegrations. For a givenelement various nuclides, characterized by the different mass oftheir nucleus (due to the different number Of neutrons) or isotopes,may be recognized. Intermediate nuclides in a radioactive seriesof disintegrations are called radioactive daughters. The naturallyoccurring series are the uranium, thorium and actinium series.The disintegration of an unstable isotope is a random eventappearing with a certain probability per unit time. A half-life of aradioactive nuclide is the time required for a given amount of elementto decay to half its initial value. The half-life is a constant for anuclide and may vary according to the characteristic of the nuclide,from a small fraction of a second to several thousand million years.The activity of a radioactive sample is determined by the number ofdisintegrations occurring per unit time (see section 1.1.5).1.1.5. UnitsThe question of radiological units is under continuous considerationby the <strong>International</strong> Commission on Radiological Units andMeasurements (ICRU). This commission has stated that the additionof further units in the field of radiation dosimetry is undesirable and


This publication is no longer validPlease see http://www.ns-iaea.org/standards/has recommended that the use of each special unit be restricted toone quantity as follows:radrCntgencurieremfor absorbed dosefor exposurefor activityfor dose equivalentThe unit for absorbed dose - the rad - is defined as the amountof energy imparted to matter by ionizing particles per unit mass ofirradiated material at the place of interest. One rad corresponds to100 ergs per gram.The former term 'exposure dose' has been replaced by the term'exposure', expressed in rCntgens (R). The unit rCntgen (R) is thatquantity of ionizing radiation which will produce one electrostaticunit of charge in one cm 3 of air (or 0. 001293 g of air).Another important aspect of irradiation is the dose rate, whichis the dose delivered per unit time. For the biological end-effectit is important to consider not only the total dose but also the doserate.The curie (Ci) is the unit of activity of radioactive nuclides andis defined as the activity of that amount of a substance which undergoes3. 7 X 1010 disintegrations per second.It is important always to make a distinction between activitymeasured in curies and dose measured in rtfntgens or rads and evaluatedin rems. Activity is equivalent to number of disintegrations perunit of time, dose is a measure of energy absorbed at some point intissue.From the point of view of radiation protection it is important totake into consideration "LET - dependent factor by which absorbeddoses are to be multiplied to obtain.......... A quantity that expresseson a common scale for all ionizing radiations the irradiation incurredby exposed persons. The name recommended for this factor is thequality factor (QF). Provisions for other factors are also made.Thus a distribution factor (DF) may be used to express the modificationof biological effect due to non-uniform distribution of internallydeposited isotopes. The product of absorbed dose and modifyingfactors is termed the dose equivalent (DE).......... The unit ofdose equivalent is the 'rem '. The dose equivalent is numericallyequal to the dose in rads multiplied by the appropriate modifyingfactors" (ICRU [3]).9


This publication is no longer validPlease see http://www.ns-iaea.org/standards/1.2. BASIC INFORMATION ABOUT RADIOBIOLOGY1.2. 1. Action of ionizing radiation1.2. 1. 1. Primary physical events in living matterAs has already been stated, the absorption of ionizing radiationby living matter is followed by the formation of ionizations and excitations;matter is permeated by electrons of different velocities. Aconsiderable number of atoms and molecules become more reactivewith respect to other atoms or molecules. Rearrangements in theexcited atoms and molecules lead to primary products in the formof stable or unstable molecules or free radicals. New chemical reactionswith adjacent molecules take place and this marks the endof the physical primary reactions and the beginning of secondaryreactions, more chemical in nature. At this point the biologicallyimportant macro-molecules are affected and the result may be someinjury of cellular function(s) and structure(s). This is the biologicalstage of the radiation reaction.1.2.1.2. Direct and indirect effects of radiationThe absorption of a quantum of radiation may result in a directmodification of the structure of a biologically important molecule, aprocess which may then lead to further changes that can becomeapparent. The direct effect is readily observed in dry material.The indirect effect may occur, taking the form of the decompositionof water or of organic molecules occurring in living matter, withthe result that either short-lived radicals (e.g. H\ OH*, HOj) orlong-lived organic radicals, which may survive up to weeks ormonths, are produced. OH* radicals can combine to H2Os and H* toH 2 . The yields of these reactions depend on LET because higherLET gives rise to greater amounts of free radicals. Oxygen reactswith H’ and forms the radical HOj which in turn combines in HgOgand Os . The technique of the electron spin resonance enables thestudy of free-radical formation in living cells.In both direct and indirect effects, a chain of chemical reactionsis induced which may result in a significant biological effect.It is not yet possible to evaluate the relative importance of directand indirect effects. It seems probable that they may be com plementary.Generally speaking, it is accepted that the indirect effect10


This publication is no longer validPlease see http://www.ns-iaea.org/standards/is due to chemical reactions'outside the sensitive molecule - the'target1. The damage to the target is secondary and therefore couldbe influenced by oxygen or protective agents. The presence of oxygenmay give rise to very active free radicals and may enhance the radiationeffect. On the other hand, the protective substances are scavengersof free radicals and their resulting action is thereforerestorative.With incorporated radioactive nuclides another effect besidesthe radiation effect may be important. The emission of radiation isoften accompanied by recoil effects or transmutation into an atomhaving new chemical properties. For example, incorporated radioactivephosphorus 32P is transmutated to 32S and this chemical changein an important place in a macro-molecule may have serious consequencesfor the vitality of the cell.If the transmutation takes place in a critical molecule such asthe molecule of desoxyribonucleic acid, important biological effectsmay follow, as was observed with 32P incorporated into the geneticmaterial. Transmutation should be considered as a factor in thetoxicity of internal emitters.1.2. 1.3. Relative biological effectiveness of different kinds ofradiationThe distribution of the ionizations in the tissue is of importancefor an understanding of the biological effect of ionizing radiation.As the ultimate transfer of energy is carried by a charged particle,the loss of energy along its path is proportional to the square of thecharge and inversely proportional to the velocity. Linear energytransfer (LET) is equivalent to the linear loss of energy and ismeasured in keV//jm. We shall see that at a given dose the.biologicaleffect may vary according to the quality of radiation used. In otherwords, radiations producing different ion densities may have differentbiological effectiveness (RBE).We have observed that different kinds of radiations have differentspatial distributions. If one ionization in a biological structure issufficient to cause change, then a radiation with low ion density willbe more effective (produce more damage per unit of absorbed dose)than radiation with high density (e.g. alpha rays) because in the lattercase many ions will be wasted. We say that the relative biologicaleffectiveness (RBE) of radiations depends on their linear energytransfer (LET).11


This publication is no longer validPlease see http://www.ns-iaea.org/standards/In reality the state of matters is not so simple and many otherfactors are involved which change the final result.It should be borne in mind that RBE is a radiobiological conceptand that in protection work quality factors are used (see section 1.1.5).Recommended values for the relationship between QF and LET aregiven in Table II.TABLE II. RECOMMENDED VALUES FOR THERELATIONSHIP BETWEEN QF AND LETLETk eV /fim in water3. 5 or less 13 .5 - 7 1 - 27 - 2 3 2 - 523 - 53 5 ' 1053 - 175 10 - 201. 2. 1. 4. Phenomena of radiation injuryRadiation injury is a complex process. The living cell is a verycomplex entity of intricate structure where a complicated series ofevents continually takes place. Radiation acts randomly on differentparts of this system. The relative importance of the part impairedby the radiation determines whether or not the cell is injured ordestroyed. For this reason the first apparent stage of radiationinjury must be sought in changes of the important macro-molecules.1 .2 .1 .4 .1 . Effects on m acro-m olecules of proteins and nucleicacids. A whole range of. biologically important substances, such asenzymes, proteins and nucleic acids, are decomposed in vitroby relatively large doses of radiation. In certain cases direct actionis exerted on the intra-m olecular bonds; in others, however, theaction is indirect through the medium of radicals. In this latter way12


This publication is no longer validPlease see http://www.ns-iaea.org/standards/some enzymes are inactivated. In the case of nucleic acids, modificationshave been observed to occur in certain characteristics,viscosity for example, even after the radiation has ceased. Themajority of macro-molecules forming important cellular constituentsare, however, quite resistant in vivo. This is particularly true ofproteins and of some enzymes, which at the same time are quitesensitive in dilute solution in vitro. On the other hand, the nucleoproteinmetabolism in the cell seems to be modified even by smallradiation doses. The end effect of radiation, it should be borne inmind, is a highly complex event as altered individual componentsinteract, causing new qualitative changes.1.2. 1 .4 .2 . Bacteriophage as models for understanding radiationeffects. Bacteriophage are in essence m acro-m olecules of proteinand nucleic acid. They have a complicated structure but are able tomultiply only in the presence of a living bacterial cell. Outside thecell they have no metabolism of their own. Their genetic apparatusis very complicated. They are able to multiply inside the host celland may be used as a model for the replication of some sub-cellularstructures, e.g. the chromosomes, ribosomes etc. All these c ir ­cumstances suggest the possibility of using phage as models of thefundamental biological action of radiations.When phage are irradiated either outside or inside the bacterialcell, they are inactivated to a degree which depends on the size ofthe dose. Generally the mean inactivation dose is in the range of105 rads. If host cells are heavily irradiated and then infected withnon-irradiated phage, they are still able to support phage growth.The nucleoprotein of the phage itself must be affected by the radiationin order to stop effectively the multiplication of the phage. A veryinterestingfact can be observed when several inactivated phage infectthe same cell. Under such conditions, the phage can recombine theirintact parts within the host cell and form a new phage capable ofreplication. This is a remarkable way of repair of radiation injuryon the molecular level.1. 2 . 1. 4. 3. Morphological changes in the cell. After irradiation acharacteristic change may occur both in-the cell nucleus and in thecytoplasm. In the dividing nucleus, chromosome breaks occur followedby normal or abnormal recombination of the broken ends(aberrations). If these changes take place in gonadal cells, hereditarychanges simulating mutations may ensue. Sometimes after ir-13


This publication is no longer validPlease see http://www.ns-iaea.org/standards/radiation the chrom osom es stick together and are afterwards unevenlydistributed during subsequent cell division. The quantitativestudy of chromosomal aberrations in man, using new techniques fortheir identification, is of considerable importance for studies ofdose-effect relationships.In many cases the nucleus and the cytoplasm increase in volume,vacuoles are formed, and, after large doses of radiation (severalhundred rads), collapse of the entire cell structure ensues. Of thevariety of particular structures, the mitochondria are very importantfor cellular respiration which releases a substantial part of energyused in biochemical reactions. Mitochondria are also connectedwith lipid metabolism. After irradiation the mitochondria increasein volume and show an alteration in staining qualities.1.2. 1.4.4. Functional changes in the cell (division). A sensitiveindicator of post-irradiation change is a delay in cell division. Thisis particularly the case when the cells are irradiated before divisioncommences. There is a critical point during cell division when thechromosomes become visible and the nuclear membrane and nucleolusdisappear. Mitosis is stopped when the cells are irradiated beforethis critical point, but is relatively less affected after this stage haspassed. The final outcome depends on the dose delivered. Somevariations of this scheme are observed when different types of cellsare studied.The delay of cell division may be due to the inhibition ofdesoxyribonucleic acid synthesis, but interference with other factorsmust also be taken into consideration. In some cases cell division vmay be more sensitive than DNA synthesis.The growth rate of cell cultures is affected under chronic irradiation.Giant cells appear with increased volume and ploidy. Thegrowth rate of Phycomyces sporangiophores is slowed down by extremelylow doses (0.001 rad).In conclusion it may be said that rapidly dividing cells are moresensitive to radiation than are non-dividing cells (with the exceptionof non-dividing lymphocytes).1 .2 .1 .4 . 5. Occurrence of mutations . Irradiation of the nuclearstructure of sexual cells induces mutations which manifest themselvesin subsequent generations and are generally deleterious.It is now a generally accepted hypothesis that genetic informationis carried in the chains of the macro-molecules of desoxyribonucleic14


This publication is no longer validPlease see http://www.ns-iaea.org/standards/acid which are integrated into the complicated structure of thechromosomes. According to this hypothesis, genes, the determ i­nants of inheritable characters, are more or less identical with asequence of nucleotide pairs in the chain of desoxyribonucleic acid.A change in the sequence of nucleotide pairs constitutes a point mutation.On the other hand, when a whole part of a chromosome ischanged through breakage of chromosomes or abnormal reunions, achromosome mutation takes place.To a very small degree mutations occur spontaneously, i.e .from unknown reasons. The overall frequency of mutations is increasedby irradiation of the germ cells. Many factors influencethe final result.. Of primary importance is the absorbed dose ofradiation and the rate of dose delivery. The stage in the developmentof the germ cells is also decisive. The increase of the fr e ­quency of mutations for any site (locus) of a chrom osom e pair isalways small, even when the highest sub-lethal doses in experimentalanimals are used.Some studies with Drosophila indicated that the frequency ofmutations is directly proportional to the dose absorbed by the gonads.In later studies it was observed that the proportionality factor varieswith the stage of the irradiated germ cells and with the delivery rateof radiation. When the same total dose is given at low dose rate,fewer mutations are induced than when a high delivery rate is used.These facts, which were substantiated by irradiation of large populationsof mice, point to the presence of a repair process. On thebasis of experiments with unicellular organisms, it is believed thatafter the primary physical event there is some time lapse duringwhich the process of mutation is not definitively established and maybe interfered with by repair action. When fully established, themutation can be reversed only by back mutation (reverse mutation).This may occur spontaneously or by irradiation of the mutant. Inany case it is a rare event and is not a practical recovery process.The present evidence suggests that ionizing radiation may producehereditary damage even at the lowest doses and dose rateswhich have been investigated. As regards man it should be bornein mind that up to the present there is little data on hereditarydamage after irradiation. On the other hand, all the experimentalevidence with other organisms proves a dose dependency. It is difficultto believe that man is an exception to this. On the other hand,animals of different species show variation in their sensitivity to themutagenic action of radiation. Further careful studies are necessaryto establish the sensitivity of man in this respect.15


This publication is no longer validPlease see http://www.ns-iaea.org/standards/1.2. 1.4. 6. Effects on embryonic development. Ionizing radiationhas a deleterious effect on developing embryos. The consequencesof damage in the developing embryonal system are amplified in thelater stages of the development and may result in malformation inthe adult stage. If the embryo is irradiated during early development,such malformations may occur in eyes, brain, medulla andalso in kidney and liver. During later embryonic development theirradiation causes abnormalities of the skeleton. When higher dosesare applied, prenatal death ensues. In man the first three monthsof pregnancy during which organogenesis occurs are most importantfor the development of malformations due to irradiation.1.2. 1.4. 7. Lethal effects. Different types of organism have verydifferent radiosensitivities. For mammals the radiosensitivity,expressed as LD 50/30 (survival of 50% of the animals 30 days afterwhole-body irradiation), varies from 400 rads for the guinea pigto 800 rads for the rat. The best estimate for man is around 500 radsafter whole-body irradiation. The individual parts of the human bodyare able to withstand comparatively high radiation doses, a circumstanceof which advantage is taken in therapy.Cold-blooded animals are generally more radioresistant, ascan be seen from Table III. The 50% survival dose for the snail isabout 20 000 rads; for bacteria the dose ranges from several thousandrads up to 50 000 and more. Phage, viruses and some protozoa areeven more radioresistant.There are several possible explanations for this phenomenon.The generally accepted hypothesis of Bergonie and Tribondeau isthat rapidly dividing tissues are generally more sensitive than tissuesin which the mitotic rate is slow. To a certain degree genetic factorsplay a role. For example, different strains of mice have differentradiosensitivity (about ± 30% of the mean quoted above). The sameholds true for bacteria and other m icro-organism s. Lately someexperiments have been performed to prove that certain radioresistantbacteria contain in their cells radioprotectors, while theradiosensitive strains are devoid of them.Another explanation of different radiosensitivity may lie in thecircumstance that some organisms have in their tissue a low oxygentension and that this could account for their higher radiosensitivity(see also section 1.2. 2. 2, role of oxygen).Up to now we have discussed radiosensitivity to whole-body ir ­radiation. Quite another result is obtained if the radiosensitivity of16


This publication is no longer validPlease see http://www.ns-iaea.org/standards/TABLE III. RADIOSENSITIVITY OF DIFFERENTORGANISMS TO X-RAYS (LDrJV 5 0 'A bsorbed dose (rad)T o m a to bushy stu n t virus 4 5 0 0 0 0B a c te rio p h a g e T 2 4 0 0 00E s c h e ric h ia c o l i B 4 0 0 0D ip lo c o c c u s p n e u m o n ia e 3 0 0 0 0A m o eb a 100 000,Wasp 1 00 0 0 0S n a il 20 0 0 0G o ld fish 850Frog 7 0 0B a t 15 0 0 0M ouse 5 6 0Rat 8 00G u in ea p ig 4 0 0R ab b it 7 0 0H a m ster 8 00D og 2 6 0Burro 3 0 0 (y -r a y s )Sw in e 2 50G o a t 2 4 0M o n k ey 5 4 0M an 4 0 0 (y -ra y s )different tissues is compared. Normal human lymphocytes showabout 15% lethality after a dose of 2 rads. Most human cell linescultivated in tissue cultures have a mean lethal dose of about 50-17


This publication is no longer validPlease see http://www.ns-iaea.org/standards/100 rads. In Fig. 3 the ranges of doses for different biological effectsin experimental animals are indicated. It is apparent that, amongmammals a great variety of responses exists for different functionsand different tissues.------------------1— — --------r— i— i— ' ' ' |-------------------1---------- --------1 . , . . . j ---------1............................................IMPAIRED FOETAL DEVELOPMENT - IN TR A UTER IN E DEATH■ * ---------------■*------------------------------------------------------------------------------------------------ HIGHER DOSES LETHAL TO MOTHERCATARACT PRODUCTIONHAEMATOPOIETIC DAMAGE f ANIMAL DIES--------------- ------------------------------------------------------------------------------------------------------------------------------------------------ ► < BEFORES TER ILITY U e^ 15 °E‘DECREASE IN LIFE-SPAN A F TE R SINGLE EXF OSURE------------------ -- ----------------------------------------------------------------------» ani MALSSPLEEN AND THYMUS, WEIGHT LOSSRAT INTESTINE. WEIGHT LOSS— m » .MAMMALIANL D 50 RANG EMOUSE BODY. WEIG HT LOSSFAIL TO SURVIVEACUTE EXPOSUREHIGHER DOSES PRODUCENO FURTHER DECREASECIRCULATORY CHANGESIMPAIREDKIDNEY FUNCTIONLIVERDAMAGECNS DAM AGEPANCREATIC"" D a m a g e10 100 1000 10000RONTGENSFIG. 3. Sensitivities o f different organs and functions to ionizing radiation. The dotted linesindicate that an effect at smaller doses is possible [5 ],1.2. 1 .4.8. Shortening of life- span (see also sections 1. 2. 1. 5. 3,1. 3 .2 .2 , 1.3. 2. 3). Experiments with animals have convincinglyshown that even relatively low acute doses of radiation, which donot produce typical radiation sickness, may lead to a reduced lifeexpectancy. The median survival time is shortened with increasedexposure (e.g. life-shortening effect in the mouse varies from about0.5 to 2% of the mean life expectancy for a dose of 100 rads [4]).Practically nothing is known about the lesions shortening life-spanin organisms. Different strains of mice differ in their life-tim eshortenings. There have been attempts made to explain radiation18


This publication is no longer validPlease see http://www.ns-iaea.org/standards/life -s h o rte n in g as a m utational p r o c e s s in som a tic c e lls . At thep resen t tim e it is d ifficu lt to p rovid e a sa tisfa cto ry explanation o fthis phenom enon as it is always c lo s e ly connected with p rob lem s ofsen escen ce which are not w ell understood. Irradiated anim als d e ­velop som e of the diseases prevalent in the sp ecies e a rlie r than nonirradiatedones and show signs of general early sen escen ce.L ife -sh o rte n in g e ffe cts o f radiation in man have not up to nowbeen dem onstrated. T here is con flictin g evidence am ong m ortalitystudies o f US and B ritish ra d io lo g ists, the m orta lity ra tes in thefo r m e r being sligh tly h igh er than in the g en era l m ale population,probably due to different ra d iologica l p ra ctice s. D oses higher than200 rads o f w h ole-b od y irra d ia tion m ay cau se a life -sh o rte n in g inman, but the effects o f lon g-term , lo w -le v e l irradiations are in thissense uncertain.1 .2 . 1 .4 . 9. Induction o f tu m ou rs. It has been establish ed beyonddoubt that m alignant tum ours m ay be induced by radiation in m osttissu e s after what m ay be a c o n s id e ra b le latent p e rio d . F o r thisrea son , if the a vera g e p eriod fo r the m an ifestation o f the tum ourgenerally exceeds the life-sp a n o f the animal, no effect is observable,because there is no tim e fo r the developm ent of the tum our.R adiation m ay induce m alignant grow th a lso through in d irectm echanism s. Pituitary tum ours may be induced through the ir r a d i­ation o f the thyroid.In som e experim en ts on the induction o f tum ours in rats thed o s e -e ffe c t rela tion sh ip can be lin e a rly extrapolated to v e ry lowd o se s, assu m ing p ra ctica lly no th resh old . In oth er ex p erim en ts,there are indications that som e kind o f threshold dose exists belowwhich tum ours are not induced during the existin g life -sp a n .1. 2. 1. 5. R elation between dose and effect1. 2. 1. 5. 1. The problem o f threshold d ose. In estim ating probableradiation injury, it is important to con sid er the d ose -e ffe ct relation ­ship at low d o se s. It is o f in terest to know whether it is feasible toextrapola te from a lin ea r rela tion sh ip to the re g io n o f e x tre m e lylow d oses, i . e . indicating that any d ose, how ever sm all, p rod u cesa p roportion al effe ct. In such a ca se , no threshold ex ists and it isto be exp ected that natural radiation m ay p rod u ce a p ro p o rtio n a leffect. The linear relationship between dose and effect is valid overa wide range fo r v iru ses, b acteria and other unicellular organ ism s.19


26Table 6-2. Fracture-specific EC in borehole KR19 (measured in 2003).Upperend ofsection(m)Lowerend ofsection(m)Measuredfracture (m)EC of fracture specific water(S/m, at 25 °C), last point intime seriesEC of fracture specific water (S/m, at25 °C), average of 10 last points intime series460.67 462.67 462.40 3.569 3.570457.17 459.17 458.40 3.549 3.549454.77 456.77 456.70 3.556 3.555460.17 465.17 462.40 3.501 3.5016.9 Borehole KR19BThe flow measurements in borehole KR19B were performed in September 2002.Measurements in natural conditions were not performed, and head values couldtherefore not be calculated. Both 2 m and 0.5 m sections were measured with pumping(see Appendices 2.1.1 and 2.1.2). A result for pressure measurement is not presented.Section- (Appendices 2.2 – 2.4), and fracture-specific (Appendices 2.5 and 2.6)transmissivity values were calculated for the results on the basis of drawdown. Theresults were compared in Appendix 2.7. The largest differences were found between thedepths of 12.26 – 14.26 m and 20.26 – 22.26 m.The pumping rate was approximately 25 l/min (1500000 ml/h), which is consideratelyhigher than the sum of the measured flow rates (approximately 3 l/min i.e. 180000ml/h), see Appendix 2.8. It is therefore assumed that there are one or numerous flows inthe borehole, outside the depth range measured, at the top or at the bottom.Separate measurements for electric conductivity were not performed. The electricconductivity and temperature were measured in connection with the difference flowmeasurements, see Appendices 2.9 and 2.10. The lower rubber disks were in placeduring these measurements, which affects the quality of the measurement results.6.10 Borehole KR20Borehole KR20 was measured in September 2002 during pumping only, which rendersthe calculation of head values impossible. The entire borehole was first measured with a2 m section length after which the flow locations were checked with 0.5 m sectionlength (Appendices 3.1.1 – 3.1.23). Section-specific (Appendices 3.2 – 3.4.6) andfracture-specific (Appendices 3.5 – 3.6.2) transmissivity values were calculated on thebasis of the drawdown. The results are compared in Appendix 3.7.Water level and pumping rate were registered during flow logging, see Appendix 3.8.The pumping rate was between 13 and 15 l /min (i.e. 780000 – 900000 ml/h). The sumof section flow rates is 6.16 l/min (369622 ml/h) and fracture flow rates 9.37 l/min(562205 ml/h). The difference between the pumping rate and the measured flow rates isrelatively large. The reason for this remains unknown.


This publication is no longer validPlease see http://www.ns-iaea.org/standards/ionizations and excitation s) is needed to produce an effe ct. In sucha ca se, the d o s e -e ffe c t cu rve takes the sigm oidal form (see F ig . 5).On the other hand, from purely th eoretica l con siderations it is p o s­sib le to assu m e that at the m o le cu la r le v e l the p r o c e s s is inducedby one p rim a ry event, i . e . without a threshold, but the subsequentre co v e ry actions m odify the final outcom e and the d o se-e ffe ct curveappears with a threshold. The chain o f events between the prim aryaction o f radiation and the final observable b iolog ica l effect is verycom plex and is influenced by many m odifying fa ctors. In such casesa real threshold, if it exists, may be masked by these com pensatoryfa ctors.R A D IA TIO NDOSEFIG. 5.Sigmoidal curves showing relation between dose and inactivation of cells requiring numbersof hits for inactivation. Cells represented by curve 1 require 1 hit, those represented by curve 2require 2 hits etc.Although the rela tiv e num ber o f individuals a ffected by sm alldoses of radiations may be extrem ely sm all, the final consequencesare im portant fo r such individuals.The problem o f a threshold dose fo r the radiation effects in manis v ery con tro v e rsia l and it is alw ays n e ce ssa ry to co n sid e r everysingle effect separately. This is esp ecially im portant in stating thep erm issib le d oses fo r individuals (see part 3).21


This publication is no longer validPlease see http://www.ns-iaea.org/standards/1 .2 .1 .5 . 2. D ose -e ffe ct relationship fo r early e ffe cts . D oses greaterthan 10 000 rads cau se in m am m als severe brain in ju ries, follow edby death in minutes o r h ours. The relationship between high exp o­sure and median su rvival tim e in irradiated m ice is exponential(F ig. 6).DOSE (103 R)FIG. 6. Relationship between high exposure and median survival time in irradiated m ice [6 ],• 250-kVp X-rays O fission neutrons X thermal column radiationF o r the exposure range 1200- 10000 R death is caused by injuryto the intestines ('in testin al sy n d rom e'). In this range there seem sto be no dependence o f su rvival tim e on exposure (see F ig. 7). Withlo w e r d o se s the su rv iv a l tim e is co n sid e ra b ly in c r e a s e d . In thisrange o f ex p osu res (< 1000 R) death is cau sed by in ju ry to theh aem op oietic system (e s p e c ia lly to bone m a rrow ) with an a c c o m ­panying secon d a ry in fection .F igu re 7 dem onstrates quite cle a rly that it w ill be futile to lookfo r a sim ple d o s e -e ffe c t relation sh ip in the d ose ran ges tested.D ifferent doses develop different m orp h ologica l and functional changesin irra d ia ted an im als. T he fin al d o s e -e ffe c t cu rv e (F ig . 7) is theresu lt o f a ll th ese co m p le x rela tion sh ip s.22


This publication is no longer validPlease see http://www.ns-iaea.org/standards/On the oth er hand, in a few in stan ces sim p le d o s e -e ffe c t r e la ­tionsh ips a re found. F o r exam ple the atrophy o f d ifferen t org a n sis m anifested in lo s s o f body weight. The dependence is lin ear notonly fo r extern a l irra d ia tion but in som e c a s e s a lso fo r in tern allydeposited ra d ion u clid es. L inear dependency is valid also fo r intestinalatrophy.1 HAEMATOPOIETICDEPRESSIONG I - TRACTDENUDATION1 CENTRAL NERVOUSSYSTEM DISRUPTIONDOSE (rads)FIG. 7. Relationship between acute whole-body dose o f ionizing radiation and median survivaltime o f m ice, rats, monkeys and presumably o f man [4 ] ,■ man • monkeys O rats and m iceIn som e ca s e s (weight o f spleen and thym us) the lo s s o f weightis lin early related to the log o f d ose. In other ca se s the final curveis com posed of two com ponents, one linear and the other exponential(the sensitivity o f lym phatic tissu e).V e ry com p lex re sp o n ses m ay be o b serv e d in su p p re ssio n o fm itotic activ ity a fter irra d ia tio n . If the rea p p ea ra n ce o f m ito sisafter irradiation is taken as an index o f the effect, then a v ery com ­plicated relationship ensues (F ig. 8).23


This publication is no longer validPlease see http://www.ns-iaea.org/standards/1. 2 . 1. 5. 3. D ose e ffe ct rela tion sh ip fo r late e f f e c t s . One o f thebest-kn ow n late e ffe c ts is ca ta ra ct fo rm a tio n . A fte r irra d ia tio n ,abnorm al ce lls a rise which rem ain inside the lens and form cen treso f op acity. N eutrons are ex trem ely e ffe ctiv e in this sen se and anexposure of 5 - 15 rads o f neutrons was su fficien t to cause radiationcataract among Japanese bomb su rv iv ors. The relationship betweenexposure and degree of lens opacity in the rat is illustrated in F ig. 9.DURATION OF IRRADIATION (h )FIG. 8. Changes in m itotic index (i.e . proportion o f cells in mitosis) o f chick fibroblasts in tissueculture cells following irradiation [ 6 ],A nother late e ffe ct o f irra d ia tion is life -sh o rte n in g . E x p e r i­m ental anim als exposed to continuous irra d ia tion throughout th eirlife -s p a n g en era lly show a life -s h o rte n in g . A lin ea r rela tion sh ip(F ig . 10) is obtained if the p e r-ce n t reduction of life -sp a n is plottedagainst dose rate (r a d /d ). It is in terestin g that irra d ia tion withneutrons is apparently e ffe ctiv e at v e ry sm a ll d ose ra tes.The data fo r leukaem ia induction am ong the H irosh im a andNagasaki su rvivors indicate that in the range between 100 and900 rads the average rate of in crea se of the incidence with dose was1. 1 ca ses p er m illion p er y e a r p er rad at H iroshim a and 1 .6 ca se s2 4


This publication is no longer validPlease see http://www.ns-iaea.org/standards/p er m illion p er y e a r p er rad at N agasaki. The relation o f averageincidence of con firm ed leukaem ia to dose in rads is plotted in F ig .ll.The relation sh ip is roughly lin ea r fo r both c itie s but the rangeo f e r r o r s is con sid era b le. Between 10 and 100 rads the in ciden cesfo r the two citie s do not d iffer sign ifican tly.NEUTRONS: NEUTRONS: NEUTRONS:DOSE(rads)FIG. 9. Relationship between exposure and degree o f lens opacity [6 ],1. 2. 1. 5. 4. The im p orta n ce o f d ose rate. A given dose, m ay bedelivered o v e r different tim e in tervals, i . e . at different intensities.The exponential d o s e -e ffe c t cu rv e is in m ost ca s e s not affected byapplying the sam e dose with differen t dose rates, becau se separatep rim a ry events act independently. If, on the oth er hand, sfeveralevents are needed in a very short tim e interval to produce an effect,a given dose b ecom es le ss effectiv e when p rotra cted . The reasonfo r the dim inution o f the final effect lies in the re cov e ry p r o c e s s e swhich take place at low radiation intensities. In the case o f theinduction o f certa in ch rom osom e a b erra tion s, fo r exam ple - likech rom osom e exch anges w hich need two sim ultaneous ch rom osom e25


This publication is no longer validPlease see http://www.ns-iaea.org/standards/brea k s - m ore exch anges p er unit d ose are obtained with h igherradiation in ten sities.A nother fa cto r co m e s in play when the ra d iosen sitiv ity o f theirradiated ob ject changes rapidly with tim e, as in the m itotic cy cle .The irradiation effect is different accord in g to whether the m oresensitive o r the m ost resistant stage o f the cy cle is affected.100806040© □2000.1 1 10100DOSERATE (rad/d)FIG. 10. Reduction o f median survival tim e in m ice exposed daily to X - and gamma radiation(solid symbols) and to fast neutrons (open symbols) [7 ],• Henshaw; ▲ Henshaw et k l .; ▼ Lorenz; ■ Upton et a l .; © Evans; O Neary eta l.;□ Upton et a l .; A Henshaw. (For references see original paper.)The im portant d iscov ery was made that low dose rates are lesse ffe ctiv e p e r rad in p rod u cin g m utations in m ou se sp erm a togon iaand odJcytes than high dose rates. It is probable that som e kind o fre p a ir in prem utational dam age is in volved at low d ose ra tes.D ose rate is a fa cto r o f great im p orta n ce in radioth erapy.F igure 12 dem onstrates that fo r a given clin ical effect a much highertotal accum ulated d ose is n e ce ssa ry if the p eriod o f irra d ia tion isp rotra cted .26


This publication is no longer validPlease see http://www.ns-iaea.org/standards/DOSE (rads)FIG. 11. Average incidence o f leukaemia in relation to dose [ 8].TOTAL ACCUMULATED DOSE(R)SKI 4 NECROSISI\\\CURE OF SK(IN CARCINOM/_____________ SKIN ERYTHEK IA_______ -------SINGLE 0-5 1 2 5 10 20 50EXPOSURETOTAL PERIOD OF RADIATION TREATMENT (d)FIG. 12.Relationship between increasing dose o f radiation and increasing period o f irradiation toobtain the same clin ica l effect [ 9 ].27


This publication is no longer validPlease see http://www.ns-iaea.org/standards/1.2 . 1 .5 . 5. Whole-body and partial-body irradiation. Lethal dosesfo r w h ole-b od y irra d ia tion (e .g . L D 50 valu es) are g en era lly m uchlo w e r than fo r p a rtia l-b o d y irra d ia tion . S u cce ssfu l radioth erapyis based on this circu m sta n ce. But there are exceptions to this rulesin ce som e org an s a re rela tiv e ly m o re sen sitiv e and re sp o n sib lefo r radiation dam age ( e .g . intestine and h a em op oietic apparatus;and therefore shielding o f bowel and bone m arrow prolongs survival).Table IV shows the effects and sign ifican ce of various radiationd oses. It can be seen that there is a con sid era ble d ifferen ce in theresu lts o f lo c a l o r w h ole-b od y e x p o su re . T h is is b eca u se duringw h ole-body exposure slight in ju ries in d ifferen t organs are integratedand the acute radiation syndrom e resu lts.F o r v e ry sm a ll d o ses o f natural radiation (c o s m ic ra y s, theradiation from radioactive substances contained in the earth 's crusto r p resen t in the human body), it is not d ifficu lt to show that theprobability of ob servable effects at the level of natural radiation isv ery low and it w ill be n ecessa ry to study an extrem ely large populationto dem onstrate any sign ifican t e ffe cts . Other fa cto rs o f thehuman environm ent com e into play and may produce sim ila r effects(ch em icals, heat etc).T A B L E IV . E F F E C T S AND SIG N IFICAN CE OF VARIOU SR A D IA T IO N DOSES IN M ANDose o f single exposure toX - or gam m a-radiation(rad)Expected e ffe ct orb io lo g ica l significanceLocal exposure3000 Tumour dose in radiotherapy3000 Skin necrosis500 - 1000 Skin erythema300 - 600 EpilationW hole-body exposure400 50°]o m ortality (y-rays)75 - 150 Blood changes and possible acute injury25 - 75 Blood changes but norm ally no severeacute injury28


This publication is no longer validPlease see http://www.ns-iaea.org/standards/1.2.2. Factors governing the biological effects of radiationF rom the p rim ary p rocess occu rrin g after the absorption ofradiation a com plicated reaction develops which may finally em ergeas a v isib le reaction to radiation. As might be expected, this chaino f reactions can be influenced in variou s ways, p articularly in m orecom p lex org a n ism s. Am ong the agents which thus govern the finalrea ction to radiation a re p h y s ic o -c h e m ic a l con d ition s, in cludingtem p eratu re and d e g re e o f h ydration , oxygen and the v a rio u s s o -ca lled p ro te ctiv e su b sta n ces.1 .2 .2 . 1. P h y s ic o -c h e m ic a l con d ition s (tem p era tu re, d egree o fhydration)In general it may be said that a low ering of tem perature reducesthe e ffe ct o f radia tion . H ow ever, in som e c a s e s (b a cte ria ) th ereexists a certain optim um tem perature fo r the reduction of the ra d i­ation effect. A lso in the case of som e anim als it has been ascertainedthat storage at a low tem perature after irradiation retards the effectwhich appears only when the tem perature again r is e s to the norm allev el. The ultim ate radiation in ju ry rem ains the sam e.S im ila rly, it m ay be said that the level o f hydration o f theorganism , sp ores, seeds etc. influences the effect of radiation. Theeffect o f radiation is in creased under conditions of in creased hydration.This is evidently connected with the production o f radicals.1. 2. 2. 2. Role of oxygenIt has a lrea d y been m entioned that in w ater solu tion H2O2 o rra d ica l O2H are form ed in the p re se n ce o f oxygen after irradiationwith X - o r gamma rays. In densely ionizing alpha p articles the localconcentration of H2O2 may attain high valu es. It is th erefore understandablethat the p resen ce o f oxygen during irra d ia tion m ay be ofim portance although the inactivation of d esox yrib on u cleic acid o r ofbacteriophage (both in dried state) seem s to be governed by a m echanismindependent of oxygen tension.Quantitative relation sh ip s betw een ra d iosen sitiv ity and oxygeneffect have been studied by s e v e r a l authors. It w as found that therelation between radiosen sitivity and oxygen tension in a suspensiono f bacteria p roceed s a ccord in g to a sim ple relation, higher con cen ­trations o f oxygen in the m edium sen sitize b a cteria to the action of29


This publication is no longer validPlease see http://www.ns-iaea.org/standards/X -r a y s . S im ilar rela tion sh ip s w ere found fo r oth er sy ste m s, fo rexample ascites tumour c e lls , ch rom osom e aberrations, and m itoticdelay in plant tissues and isolated mam malian ce lls.T he oxygen effect is usually le s s with highly ion izin g radiation,such as alpha p a rticles o r slow e le ctro n s.A v ery m arked effect o f hypoxia has been observed with ir r a d i­ated rats. The LD5o/3c>for rats irradiated in 5% oxygen is tw ice thatfo r anim als exposed in a ir. In a sim ila r way hypotherm ia has aprotective effect, probably due to decreased blood flow with resultinglow er oxygen tension. On the other hand, oxygenation may in creasethe radiosen sitivity. E xperim ents with in crea sin g oxygen p ressu reare being p erform ed in radiotherapy o f tum ours.The oxygen effect during irra d iation must not be confused withthe application o f oxygen after irradiation . In this ca se the oxygeninfluences som e stages in the developm ent o f radiation injury whichare sensitive to the p resen ce o f oxygen.F o r the understanding o f different a fte r-e ffe cts the form ation oforganic p eroxid es is im portant. Inactivation o f phage p a rticle sirradiated in broth is enhanced by the presen ce of organic peroxidesform ed in the broth during irra d ia tion . T his action m ay be ob serv a b lefo r several days after the irradiation has stopped. If inorganic p e r­oxid es are added b e fo re irra d ia tion , the sen sitivity o f phage o rb a cteria is in cre a se d .1 .2 . 2. 3. P rotectiv e substancesThe fact that it is possible to d ecrease the radiosensitivity o f theorgan ism by outside intervention has led to a search fo r substanceswhich would provide a m easure o f protection against radiation. Therange o f p rotectiv e substances o f this kind is v ery la rge, includingsubstances o f different ch em ical and physical p rop erties. The m ostim portant are sulphur-containing compounds (cysteam ine, cystam ine,am inoethyl-isothiouronium (A E T ), glutathione, e t c .) Some enzym einhibitors (sodium cyanide), alcoh ols, certain m etabolites (gluconate,A T P , pyruvate) have a sim ila r action. A noxia-producing ch em icalslike PAPP (p-am inopropriophenone) which induces methem oglobinemiaenable 72% survival in m ice after a lethal exposure.The p ra ctica l applicability o f ch em ica l p rotection in man up tonow is slight, b ecau se m ost o f the active ra d iop rotectors a re toxicin con cen tration s needed fo r sign ifican t p rotection . The abovementioned ch e m ica l p r o te c to r s a re o f p ra ctica lly no value against30


This publication is no longer validPlease see http://www.ns-iaea.org/standards/ch ron ic ex p o su re . A cute and ch ro n ic radiation in ju ry in volv e d ifferentorgans o r organ groups and they do not receive equal chem icalp rotection . A ll these fa ctors dim inish con siderably the p racticalityo f use o f different drugs in prevention o f radiation injury.1 .2 .2 .4 . R ecov eryRadiation injury is a p ro ce s s com p osed o f many stages, endingin the ex p ression of the p rim a ry dam age. Some o f these stagesare only tem porary and, in the p resen ce o f inhibitory fa cto rs, theycan be restored . It is p ossible that organ ism s have v ery varied r e ­cov ery p ossib ilities which are at present not w ell known.It is, however, possible to prom ote recov ery by giving recoveryagents o f two types after irradiation.(1) A gents w hich d estroy som e in term ed ia te com pound in thechain o f events a fter irradiation . The e ffe ct o f u ltra v iolet rays inbacteria con sists in form ation o f thymine d im ers in the m olecule ofd esoxyrib on u cleic acid. In radioresistan t bacteria an enzym e ispresen t which is able to e x cise the d im er and re s to re the integrityo f the DNA m o le cu le . In som e ca s e s changes in tem peratu re mayinhibit the e x p re ssio n o f radiation in ju ry.(2) A gents w hich a re able to rep la ce a dam aged com pound o rce ll. This m ode o f re co v e ry o ccu rs som etim es when irradiated andnon-irradiated bacteriophages in fect bacterial ce lls and the damagedparts o f the phage genom e are subsequently replaced by the 'healthy1ones from n on-irradiated phages.E xp erim en ts with la rge m ultinucleate am oeba have shown thatin lethally irradiated individuals vitality could be restored by fusionwith fragm ents o f n on -irradiated individuals.On a la rg e r sca le , whole populations o f dam aged bon e-m a rrowce lls m ay be rep la ced by in jectin g intact b on e-m a rrow c e lls from , an on -irra d ia ted d on or. T h ese experim en ts su cce e d on ly when thein jected b o n e -m a rro w c e lls are iso lo g o u s. A fter a h om ologou s o rheterogous injection an important im m unological reaction takes placedue to in com patibility between the donor ce lls and the re ce p to r anim al.T his 'secon d a ry d isea se' m ay lead to the death o f the anim al. F o rthis reason autologous bon e-m arrow transplants may be used in manto induce m ore rapid repopulation of m arrow sites, although hom ologoustransplants in a few instances have been tolerated.31


This publication is no longer validPlease see http://www.ns-iaea.org/standards/1 .2 . 2. 5. AdaptationT here is at presen t no convincing evidence that organ ism s canadapt them selves to high levels o f radiation. Experim ents perform edwith D rosophila and yeasts in a high radiation background have notyielded m ore resistant strains. In som e instances, a higher ra d ioresistan ce was ob serv ed in tum ours treated with a su b-leth al d ose.T h is fa ct m ay be attribu ted to a d e c r e a s e d le v e l o f oxygen in thetu m ou r tissu e , due to p a th o lo g ica l ch anges in the b lo o d v e s s e ls .It is , h ow ever, not im p o ssib le that som e ra d ia tion -a d a p tedorgan ism s w ill be found in geographic region s where a high level ofnatural radioactivity exists. Certain densely populated areas o f theg lobe (parts o f India and B ra zil) have an unusually high content ofradioactive substances in the environm ent. H ow ever, even if suchadaptation occu rs in the population, it is always n ecessa ry to bear inmind the influence of selection , in which the m ore resistant organismsu rvives.1. 2. 2. 6. Relative radiosen sitivityIt has been observed that the radioresistance of certain bacterialc e lls is substantially in creased by mutation. C linical experien ce inradiotherapy also indicates that som e individuals are probably m oreresista n t to radiation than oth ers. Since this ex p erien ce is basedla rg ely on the e ffe cts of p artial irra d ia tion , the sign ifica n ce o f theobservation cannot be extended to the whole body. F o r the present,we can only say that th ere is a wide variation in the d egree o fsen sitivity o f variou s organ ism s, sin ce a few rads are su fficien t tok ill lym ph ocytes, w h ereas som e hundreds o f thousands o f rads arerequ ired to kill an adult in se ct and o v e r a m illion rads to d estroyv iru s e s and b a cteria com p letely .The various organs d iffer con siderably in their radioresistan ce.Although it is not p ossib le to con stru ct an exact sca le o f ra d io ­resistan ce fo r the organs, it may be roughly concluded that the blood -form in g organ s, gonads and len ses o f the eyes are am ong the m osts e n sitiv e . M u scle, con n ectiv e tissu e and adult bone have a r e la ­tively high resista n ce to radiation. The skin, in testin es and en d o­crin e glands fall into an interm ediate category. This cla ssifica tio ncannot, h ow ev er, be exact, b eca u se sen sitiv ity depends on m anyfa ctors (physiological state, oxygen content, tem perature, etc. ) andon the method of observation, i.e. whether m orp h ological o r p h ysiolo g ica l changes are registered .32


This publication is no longer validPlease see http://www.ns-iaea.org/standards/1.2.3. C onclusionsIt should be em phasized that today's knowledge of the effects ofradiation on living organ ism s is in com plete, p rim a rily beca u se thep resen t knowledge o f biology is not su fficien t to esta blish soundc r ite ria for distinguishing injury from the norm al state o f the o r g a ­n ism . N everth eless, ou r knowledge o f radiation in ju ry fro m bothhuman e x p e rie n ce and anim al experim en t is su fficien t to m ake itp ossib le to esta blish m axim um p e rm issib le d oses o f radiation witha con sid era b le d egree o f con fid en ce that adequate p rotection isp rovid ed .1.3. RADIOPATHOLOGY1. 3. 1. Acute radiation effects1.3. 1.1. Acute syndrom eA fter irra d ia tion o f the g re a te r part o f the body, a s e r ie s ofp ath ological sym ptom s ensue, which orig in a lly w ere d e s crib e d as1rOntgen s ic k n e s s '. Only after the exp erien ce gained at H iroshim aand Nagasaki has our knowledge of the aspects and the sym ptom s ofa typical radiation d isea se been em phasized and in crea sed .B a sica lly , this d isea se can o c c u r as the acute radiationsyndrom e, resu ltin g fro m w h ole-b od y irra d ia tion by a d ose aboveabout 100 rads delivered at relatively high dose rates (several rad/h)and showing signs and sym ptom s within minutes to 30 to 60 days subsequentto exposure.Radiation d isease is caused principally by irradiation with gammarays, X -r a y s and neutrons. Alpha and beta rays e x e rcis e an effectwhen rad ioisotop es in la rge quantities have been taken into e x p erimental anim als and deposited lo ca lly .Acute radiation d isea se is ch aracterized by a latent p eriod , whichsu pervenes after in itial sym ptom s of m ala ise, lo s s of appetite andfatigue, during which the su fferer feels no other untoward symptom sand the length of which is roughly in versely proportional to the radiationdose receiv ed . At the end of the latent period, the onset of theilln ess o ccu rs: early lethality, destruction of bone m arrow , damageto the gastro-in testinal tract associated with diarrhoea and h aem orrhage,dam age to the cen tral nervous system , epilation, ra d io d e r­m atitis, drop in sp erm count and ste rility .33


This publication is no longer validPlease see http://www.ns-iaea.org/standards/Among the early signs of acute radiation disease may be vom itingwhich appears in about 50% of exposed patients after a whole-bodyexposure of 200 R (psychogenic fa ctors must be con sid ered ). Suchvom iting may be a sufficient reason for hospitalization of the patient.E a rly lethality (e x p re ssed as L D 50) m ay appear w ithin 30 to60 days after a dose between 300 and 500 rads. There are not enoughdata available to establish an exact d o se -e ffe ct relationship for man.An approxim ate relationship is dem onstrated in F ig. 13 based on d ifferentestim ates of three well-known radiation Com m ittees. A ccord ­ing to this figure the LD50 d ose of acu tely d eliv ered radiation fo rman lie s in the range o f 400 to 500 ra d s.900800~ 700V>TD flj 600L.LJ 500COa 40030020010000.01 1 2 5 10 20 40 60 80 90 95 98 99PROBABILITY OFDEATH ( °/o)FIG. 13. Probability of early death in man as a function o f acute whole-body dose [4 ],The relationship between survival time and whole-body exposureof m ice, rats and m onkeys for doses between 400 and 40 000 rads isdem onstrated in F ig . 7. The data points a re a vera ges fo r se v e ra lanim als. F or an individual animal the uncertainty factor may be asmuch as 3. The dotted curve is a rough estim ate for man based onthe few data available.The figure shows clearly the three regions corresponding to thehaem atopoietic depression , to the gastro-in testin al tract denudation(a plateau in the su rv iv a l cu rve) and the d isru p tion o f the cen tra lnervous sy stem . One m ust alw ays b ea r in mind that the cu rv e isschem atic and that the designation of the three ranges does not im plythat damage to other tissu es does not contribute to death.34


This publication is no longer validPlease see http://www.ns-iaea.org/standards/W e have already m entioned that d ifferen t parts of the anim albody are not equally sen sitive to irradia tion . This is true also forman. It is generally accepted that the trunk is relatively m ore sen ­sitiv e, e sp e cia lly in the ep ig a stric region , than is the head o r thereg ion o f the thighs.In F ig . 14 the p rob a b ility of an individual show ing p rod ro m a lsym ptom s of radiation sick n ess after a w h ole-b od y ex p osu re isplotted against dose in rads. It is assumed that 99. 9% of all subjectsexposed to 300 R w ill show acute radiation syn drom e. A lso in thisca se the hypothetical nature of the assum ptions and the inadequacyof pertinent data must be taken into con sid eration .FIG. 14.Conjectural dose-response probability relationship for prodromal response to acute radiationexposure [4 ],PROBABILITY (%»)1.3. 1.1.1. Lym phatic and haem atopoietic tis s u e s . Lym phatictissu es are among the highly radiosensitive system s. It is here thatthe lym ph ocytes, which pass into the blood and b ecom e part o f thewhite corp u scle group, are form ed. Even after sm all radiation dosesthe num ber of lym phocytes tem p ora rily falls in som e ca s e s . A fterhigh doses, the lym phatic tissue ceases to be active and the lym phocytecount in the peripheral blood falls im m ediately, the d egree anddu ration o f the d ro p depending upon the ra d ia tion d o s e r e c e iv e d .The bone m arrow , where the red corp u scles and leukocytes areform ed, is highly radiosen sitive. P articu larly liable to damage arethe im m ature blood c e lls in the p r o c e s s of form ation ; the e a rlie r35


This publication is no longer validPlease see http://www.ns-iaea.org/standards/th eir stage of developm ent, the g rea ter is th eir sen sitivity. A ftersm a ll radiation d o se s, a m od erate m u ltip lication of the young redand white cells occu rs, but after large doses an overwhelm ing effectupon the m arrow is observed , leading to the com plete depopulationof the m arrow tissu e. The m arrow begins to resum e activity in thefirst or second week after irradiation and the duration of the p rocessis governed d irectly by the radiation dose. During the p rocess itself,recov ery of white-cell production is m ore rapid than eryth rocytop oiesis.It m ay be said, v e ry b roa d ly speaking, that rea ction s to ra d i­ation as m anifested in the p erip h eral blood depend on the radiationd ose, sp ecies sp ecificity , the life-sp a n of the different corp u scu larelem ents, their sen sitivity and pow ers of renew al and the state ofthe organ ism at the tim e.Im m ediately after irra d ia tion , a sh ort p eriod of le u k o cy to sisensues, occasion ed by the relea se of leukocytes from the bonem a rrow . Then follow s a drop in the total leu kocyte count, these v e rity and duration o f which are p rop ortion a l to the d e g re e andlength of radiation exposu re. A fall in the lym phocyte count isc h a ra cte ris tic and r e c o v e r y fro m neutropenia m ay be taken as agood prognostic sign. The eosinophil count drops only after a largerd o se. The num ber of re ticu lo cy te s is a lso reduced and early r e -ticu locy tosis is a favourable indication of re co v e ry . The r e d -corp u scle count drops only very slow ly after irra d iation . M arkedanaem ia does not o ccu r until two to fou r weeks after a la rge ra d i­ation dose. In cases of severe damage this turns to aplastic anaemia.A fter irradiation, the blood-platelet count also falls, the ra d iosensitivity of the p latelets being g rea ter than that of e ry th ro cy te s.The lack of blood platelets leads to a tendency to bleeding. The r e ­covery of the blood-platelet count is generally very slow. The m onocytesbehave in the sam e m anner as eosinophils and an in crea se inth eir num ber is a favourable indication o f re co v e ry .1.3. 1.1. 2. G a s tro -in te s tin a l s y s t e m . S m all d o s e s o f ion izin gradiation affect the m otility o f the intestine and enzym e secre tio n ,whereas large doses lead to ulceration of the intestinal m ucosa. Theintestinal bacteria penetrate the dam aged intestinal tract, enter theblood system and are ca rrie d throughout the body, causing seriou ssep tic con d ition s. Changes in the g a stro -in te stin a l tra ct a re f r e ­quently d e cis iv e in the ou tcom e o f radiation d is e a s e . N aturally,d ire ct irra d ia tion fro m con sid e ra b le quantities of in gested r a d io ­active substances in experim ental anim als may severely damage theintestinal wall in a sim ilar m anner.36


This publication is no longer validPlease see http://www.ns-iaea.org/standards/1.3. 1.2. SkinSince radiation entering the body from external sou rces has a l­m ost in varia bly to p ass fir s t through the skin, the rea ction o f theskin to ion izin g radiation has been studied in great d eta il. B eforethe developm ent of accu rate d osim eters, erythem a of the skin fo l­low ing external irradiation by X -r a y s was taken as the basis of theb io lo g ica l unit o f d ose. A fter la rg e r d oses this erythem a changesto pigmentation, and after still greater doses, various types of radiodermatitis appear, which m ay lead to n e cro sis and u lcera tion s andmay finally becom e malignant growths. This latter case applies particularly to the form s of derm atitis resulting from chronic low -d oseX -r a y irradiation.T h ree d e g re e s of acute ra d io d e rm a titis can be distin guish ed:(1) R adioderm atitis eryth em atosa. This m an ifests its e lf in areddening of the skin beginning on the fourth to the seventh day. Onlyin the third to fourth week d oes the skin regain its n orm al a p p ea ra n ce.Hair from head and beard may fall from the areas of reddened skinwithin two or three w eeks. The skin rem ains tem porarily coloured,peels easily, and is d ry. E pilation is one o f the m ost con spicu ou sevents even after a dose of 200 rads of soft radiation. It begins 13 to17 days a fter irradiation and m ay be rep laced by a regrow th of hairafter several months depending on the dose delivered. A dose higherthan 2000 rads leads to com plete and permanent epilation.(2) R adioderm atitis bu llosa . T his o ccu rs after la rg e r d oses,and between the second and fifth days after exposure the skin becom esdark violet in colou r and water b listers, sim ilar to those occu rrin gin se con d -d e g re e burns, a re fo rm e d . The skin itch es, burns andis painful. Within two or three weeks, the hair falls out and the lossis largely perm anent. Healing is slow , and the skin th ereafter r e ­m a in s d ry , w h itish and c r o s s e d with b r ig h t-r e d b lo o d v e s s e ls .(3) R adioderm atitis e sch a rotica . The skin reddening appearsas early as the second or third day after a high radiation dose. Deepand painful u lce rs and a lso a b s c e s s e s appear on the skin, healingis slow, and sca rs, interwoven with large blood v e sse ls , rem ain onthe damaged a reas. The skin is dry, since the sebaceous and sweatglands have been com pletely destroyed.37


This publication is no longer validPlease see http://www.ns-iaea.org/standards/Chronic derm atitis occu rs after sm all doses (considerably m orethan the m axim um p e rm is s ib le d oses) when p erson s w orking withion izin g radiations r e c e iv e dam age to the skin, p a rticu la rly o f thehands, which becom es dry and of v io le t-re d colou r. Num erous telangiectaticareas are ob serv ed . Hair falls from the body, head andbeard, the skin b e co m e s thin, k era toses are subsequently form ed ,togeth er with w arts, betw een which the skin ea sily cra c k s . In advancedstages u lce rs o c c u r and in som e ca ses even ep itheliom ata.1.3. 1.3. GonadsThe sexual glands a re highly ra d iosen sitiv e, the m ale organ sbeing con sid era bly m ore sen sitive than the fem ale. With a d ose aslow as 25 rads to the te sticle s, either loca lly or as w h ole-body exposure, detectable d ecrea se in sperm count o ccu rs. A dose of about250 rads m ay p rod u ce te m p o ra ry s te r ility fo r 1 to 2 y e a r s . Thedose required to produce permanent sterility in men is approxim ately600 rads delivered acutely. In wom en this dose amounts to about800 rads.1.3. 1.4. E m bryonic developm entD evelopm ental abn orm alities m ay also occu r when the em bryoor foetus is irradiated. Particularly in the early stages of embryonicdevelopm ent a dose of a few tens of rads may be sufficient to produceseriou s abnorm alities. This fact is especially important when womenare irradiated during the first days of pregnancy. A number of caseso f m icrocep h a ly with con gen ita l im p lica tio n s have been o b s e rv e dam ong ch ildren who w ere irra d ia ted in the uterus during the atomb om b in g s.It m ay be m entioned that ra d ioactiv e substances can reach theem bryo and the developin g foetus during the period o f nourishm ent,via the placenta. P a rticu la rly in the early stages of em bryon ic d e­velopm ent, radion u clides absorbed in this m anner resu lt in what iseffectively a w h ole-bod y irradiation o f the em bryo.1.3. 1.5. SkeletonBone changes have long been ob serv ed in human bein gs and inexperim en tal anim als as a resu lt o f ion izin g ra d iation s. In youngindividuals th ese changes ran ge fro m cessa tio n o f the p r o c e s s o f38


This publication is no longer validPlease see http://www.ns-iaea.org/standards/o s s ific a tio n and grow th (on exp osu re to d o s e s o f the o r d e r of100 rem s) to com p lete n e cro s is of the bone, observ ed after d osesof se v e ra l thousands of re m s. The m a jority of these bone in ju rieso ccu r as a resu lt of in correct radiotherapeu tic treatm ent o r o f in ­corporation of radioactive substances into the bone. In both circu m ­stances, an in creased incidence of bone tumours has been observed.However, the only bone tumours observed in man have resulted fromthe in corp ora tion of radium into the bon e. It is estim ated that anindividual retaining 0. 1 iug 226Ra after 30 years would have probablyinitially absorbed 10 ng, the greater part of this amount being elim ­inated. In general it may be said that radionuclides deposited in thebones display a particular tendency to b ecom e loca lized in the g row ­ing parts of the bone (epiphyses). With regard to malignant tumours,it has been shown that they m ost frequ en tly d ev elop in the m e ta -p h y ses o f the lon g b on es and m any m ay o c c u r in on e in d iv id u a l.1.3. 1.6. N ervou s tissu eF or a long tim e nervous tissue was thought to be highly resistantto irra d ia tion , T his was due to the fact that after irra d ia tion onlym orph ological changes w ere sought, which require considerable dosesto becom e apparent. Recently, functional changes have been elicitedwith m uch sm a lle r and often v e ry low d o s e s . A m on g such m o d i­fication s, m ention m ay be made of d e cre a se s in excitability andchanges in conditioned r e fle x e s . Irradiation o f anim als with300-400 R produces changes in the electroencephalogram which mayp ersist for about one week.1. 3. 1. 7 . M odification of the immune statusD isturbances of the im m u nological m echanism can be producedby external and internal irradiation. In the latter case, disturbancesmay occu r when the ce lls of the reticulo-en doth elial system have incorporatedradioactive m aterial which may inhibit their im m unologicalfunction.In ex p erim en ts with m on k eys, a w h o le -b o d y irra d ia tio n with450 R resulted in a tem porary su ppression of the antibody resp on sewhen the irradiation was perform ed 24 hours before the beginning ofim m unization. This effect did not develop fully after irra d iation inp reviou sly im m unized anim als.39


This publication is no longer validPlease see http://www.ns-iaea.org/standards/1.3.1.8. Other organsM odifications to the v ascu lar system after irradiation take theform of changed p erm eability of the v e s s e ls , and m orp h ologica lchanges in the walls with circu latory disturbances (n ecroses). Thesevascular changes are of particular significance for the skin.The lens of the eye is sensitive to irradiation. D oses of 15 - 30 radsX -r a y s and p o ssib ly 1 rad o f fast neutrons cau se m inim al lensopacity in the m ou se. S everal hundreds of rads initiate tem poraryconjunctivitis in man, but exposure to 2000 R destroys rods in retinaof monkeys and 30 000 R affects all retinal elem ents m orphologically.E ndocrine glands in adult anim als are con siderably radioresistan t(thyroid gland). H istological changes in dog thyroid w ere observedafter an exposure o f 10 000 R.R adiation can a lso prod u ce certa in n o n -s p e c ific e ffe cts w hichare m ediated through the adrenal gland and which are iden tical withthose produced by other stre sse s . This em phasizes the n on -sp ecificch a ra cter of som e effects o f radiation. E ffects of this type can beobtained with a few hundred rOntgens o f X -r a y s , and it is p o s s ib lethat other en docrin e p r o c e s s e s con cern ed with regulating functionsin the body can be affected by such exposu res.T A B L E V . D E C R E A SE IN L IF E -S P A N A F T E R P A R T IA L -AND W H O L E -B O D Y X -R A Y E X P O SU R E C O M P A R E D IN THEMOUSE aRegion exposedExposure(R)Mediansurvivaltim e(d)Significantlydifferentfrom control(P g 0 .0 5 )C o n t r o l 0 676 -Entire anim al 530 582 yesEntire chest 720 646 noO n e-h a lf chest 570 654 noand caudal 1140 591 yes2 cm o f trunk 1700 525 yesa Fem ale m ice, 170 days when irradiated; with the doses em ployed there, were no acutedeaths [10, p. 1 56].40


This publication is no longer validPlease see http://www.ns-iaea.org/standards/1.3.2. C hronic and d elayed radiation e ffe c ts1.3. 2.1. G eneral c h a ra cte risticsL ate radiation e ffe cts a re g en era lly con sid ered as th ose thatappear many months or years after irradiation. They may be roughlydivided into two ca te g o rie s: effects which are caused by ch ron icirradiation with sm all d ose rate and effects follow ing acute ir r a d i­ation after a certain tim e -la p s e .It is usually d ifficu lt to distinguish betw een a late effect and ad isease induced by other causes, som e of which may be entirely unknown.When populations irradiated fo r m ed ica l reason s are con ­sidered, it should be borne in mind that the treated disease itself maysim ulate a radiation effect.Late effects may be caused by loca l irradiation of tissu es or byw h ole-b od y irra d ia tio n after a certa in p e rio d o f tim e . T he m ostim portan t late e ffe ct is the induction o f tu m ou rs.1. 3. 2. 2. L ate e ffe cts a fter lo c a l irra d ia tio nOne ch a ra cte ristic late effect is the d e cre a se in life -s p a n . Itis known that p artial-bod y irradiation d ecrea ses the life-sp a n muchle s s than w hole-body irradiation (see T able V).Induction o f len s op a city (see a ls o s e ctio n 1. 3. 1.8) throughcataract form ation m ay be the outcom e o f l o c a l irradiation. C lin icallysignificant cataracts in man may be produced by an X -r a y doseof 600 - 1000 rads. The p ro g re ss of the developm ent of the lensop a city is dependent on the s iz e o f the d o se . The fra ction a tion ofthe d o se d e c r e a s e s the in cid en ce o f ca ta ra ct and a lso reta rd s itson set. G en erally the lens op acity p r o g r e s s e s slow ly and in som eca se s a slight r e c o v e r y has been o b serv e d .Among im portant late effects are in ju ries to the skin: derm atitis,atrophy, epilation, hyperkeratosis, vascular scle ro s is, telangiectasia,etc. T hese changes m ay p ro g re ss in a rythm ic way changing fromsta g es o f r e la tiv e a m e lio ra tio n to d e te r io r a tio n and v ic e v e r s a .N ep h rosclerosis and related hypertension m ay appear as a lateeffect after ov er-ex p osu re of the kidney region. Sim ilarly, intensiveirradiation of the lungs may cause p rogressiv e fib rosis with a rteriosc le r o tic changes. It m ay be said that degen erative changes in theblood v essels together with destruction of parenchym atous cells arech a racteristic of the late effects of irradiation .41


This publication is no longer validPlease see http://www.ns-iaea.org/standards/1. 3. 2. 3. Late effects after whole-body irradiationUnder continuous w h ole-bod y irradiation at d ose rates as highas 0. 5 ra d /d , no d ifferen ce in life-sp a n between irradiated and control animals was observed (F ig. 10).D elayed in ju ries have been ob served in b lo o d -fo rm in g organ s.They m anifest th em selves in the form of aplastic anaemia orpancytopenia. E xact rela tion sh ip s betw een d ose and e ffe ct a relack ing. Am ong the su rv iv o rs at N agasaki and H iroshim a delayedin ju ries (with the exception of leukaem ia) are generally ra re . Someirradiated p erson s died from cach exy connected with d istu rban cesin the haem atopoietic apparatus.1.3. 2. 4. Genetic effectsIrradiation of the germ tissu es m ay cause mutations which appearin later generations. The follow ing features are ch aracteristicof mutations:(a) Mutations having once occu rred are permanent. The mutantgenes may be restored only by a re v e rse mutation and this has onlya slight probability o f o ccu rrin g . In the p rocess of selection som eof the mutant genes m ay be elim inated.•(b) The great m a jority of ob serv ed mutations are d e le te rio u s.(c) It has not thus fa r been p roved w hether a th resh old d o seex ists fo r m utations. T his m eans that every ion izin g radiationlocated in a germ cell should be assum ed to have a sm all statisticalprobability of causing a mutation.(d) Sm all d oses m ay be cum ulative and the end resu lt m ay notappear until many generations la ter.(e) The gen etic d o se req u ired to double the m utation ra te inman is of the ord er of 10 to 100 rads. It cannot be less than 3 radssin ce this level is attained in a human generation of 30 yea rs as theresu lt of natural radiation. However, recent work may indicate thatat low d ose rates the d ose requ ired to double the m u tation -rate inman m ay be la rg e r than indicated h ere.A whole range of ch a ra cte ristics m ay be influenced by gen eticdam age, including variou s m orp h olog ica l and b io m e trica l ch a ra c­te r is tic s (life-sp a n , weight at birth, in tellig en ce, fe rtility , lethaleffects, etc.). Owing to the uncertainty of som e of the genetic m e­chanism s in volved, it is safest to assum e that approxim ately 4% ofchildren born are at present burdened with hereditary disturbances.42


This publication is no longer validPlease see http://www.ns-iaea.org/standards/An in crea se in the level of radiation could lead to an in crea se in thisgenetic load.1.3. 2. 5. Radiation carcin ogen esisThe data on radiation ca rcin og en esis was recen tly surveyed bythe UN S cien tific C om m ittee on the effects of atom ic radiation andpublished in its rep ort issu ed -in 1964.One of the first significant late effects o f irradiation was the d e­velopm ent of skin ca n ce rs am ong ra d io lo g ists. It w as establish edlater on that there is a causal link between irradiation and incidenceof leukaem ia.It was not easy to show a relationship between radiation exposureand leu k aem ia. C onsistent data a re available m ainly fo r the s u r ­v iv ors of the explosions at H iroshim a and Nagasaki. The su rvivorshave been divided into groups a ccord in g to the estim ated d ose theyr e c e iv e d . T he estim a tes of the d o ses are a lm ost ce rta in ly not ine r r o r by a fa ctor g rea ter than two or th ree. An approxim ate p r o ­p ortion a lity o f the avera ge y e a rly in cid en ce o f rad ia tion -in d u cedleukaem ia fo r the p eriod from 1950 to 1958 was found in the rangefrom about 100 to 900 ra d s. The p robable rate o f in crea se o f in c i­dence with d ose is between 1 and 2 ca ses p er year p er rad perm illion exposed individuals. This estim ate is also valid in the rangebetween 300 and 1500 rads for induction of leukaemia among patientsirradiated therapeutically for ankylosing spondylitis.Important are the resu lts of a su rvey of induction o f leukaem iaam ong ch ild ren irra d ia ted in u te ro . U nder ce rta in con d ition s,radiation d oses of the ord er of a few rads can induce malignantgrow th. The highest risk was with m others exposed fo r diagnosticX -r a y pelvim etry during the first three months of pregnancy.The in ciden ce o f thyroid carcin om a as a result o f irradiation o f thethyroid region for therapeutic purposes during childhood is also prop ortionalin a range of d oses between 100 and 300 rads and leads to a sim ilarrisk estim ate as in the case o f leukaem ia of the atom ic bom b su rv iv o rs.A ll these resu lts indicate the p ossib ility that ionizing radiationm ay in crea se the p robability o f induction m align ancies in man andthat in som e c a s e s , p a rticu la rly am ong young individuals, the n e­c e s s a r y d ose m ay be v ery low .It should be alw ays born e in mind that many types o f tum ourso ccu rrin g in man a re, as fa r as we know, not induced by ion izin gradiation (e.g. the tum ours of g a stro -in te stin a l tra ct, o f u teru s,m am m ary tu m ou rs etc.).43


This publication is no longer validPlease see http://www.ns-iaea.org/standards/1.4. M ETABO LISM AND T O X IC ITY OF RAD IOACTIVEM ATERIALS1.4.1. GeneralR adion uclides can enter the human body by v ariou s paths andcause internal irradiation , the im portan ce of which is p articu la rlyem phasized by the fact that certain radionuclides are deposited m oreor less permanently in the body, leading to contamination which mayhave seriou s con seq u en ces fo r the affected individual. F o r thisrea son it is n e ce s s a ry to have a detailed know ledge of a ll thechannels through which ra d ioa ctiv e m a teria ls can be absorbed , ofthe fa ctors which a ccelera te this absorption, of the manner and siteso f deposition in the body, and of the rates o f elim in ation . Muchvaluable inform ation in this respect is contained in the ICRP reports [11].The physical and ch em ical properties of the absorbed m aterialsa re o f great im p orta n ce. The length of exp osu re is in flu enced bythe physical h a lf-life and other b iological param eters, and the patternof in ju ry depends on the nature of the em itted radiation. Alpha andbeta rays are absorbed lo ca lly and d e liv e r the dose to sm a ll areaso f tissu e, while gam m a rays in flu en ce la rg e p ortion s o f the bodyor may even escape the body. As already stated, the chem ical natureof the absorbed m aterial plays an important role in defining the ultimatebiologica l effect. R adioisotopes of.elem ents norm ally presentin the body (phosphorus, carbon, calcium , sulphur, iron, strontium)participate in the m etabolic p rocess and behave in the body like stableisotop es of the sam e elem ents. They may be incorporated into im ­portant b iologica l com pounds and changed during disintegration intoother elem ents which are foreign to the compound.D iffe re n ce s betw een lo ca liz e d and d iffu sed in tern al radiationm ay be of extrem e im p ortan ce. Som e radion u clides m ay be d ep o­sited and aggregated in to'h ot s p o t s '. The lo ca l doses and d ose ratesin such cases may attain high values. Hot spots com plicate also theconcept of Relative B iological E fficien cy (RBE) fo r internally depositedbon e-seekin g m aterials in the sense that not only linear energytran sfer (LET) but also factors like dose, dose rate, biological endpointetc. must be considered.1.4.2. Absorption of radionuclides1. 4. 2. 1. Absorption from the gastro-intestinal tractIngestion is im portant m ainly fo r m aterials solu ble in bodyflu id s. Some solu ble com pounds m ay be con verted to insoluble hydroxid es at the pH of body fluids and v ice v ersa .4 4


This publication is no longer validPlease see http://www.ns-iaea.org/standards/The in gestion o f ra d ioactiv e m a teria ls by m an can take p la ceeither with drinking w ater, with food, by sw allow ing of inhaled p a r­tic le s , o r by acciden tal penetration into the mouth cavity.F ood -ch ain s are of great im portance in evaluating potential con ­tam ination o f the body by ra d ioa ctiv e m a teria ls p resen t in the environm en t. One of the m ost com m on routes to man fo r ra d ioactivefa ll-ou t is as follow s:F a ll-ou t ---------* plant ---------* cattle ---------* meat (m ilk)-------- > manMilk is a v ery im portant food -ch ain path, esp ecially fo r radioactivestrontium and iodine.1.4. 2. 2. A bsorption through inhalationIn the atom ic industry the m ost usual entry of radioa ctive m a­te r ia ls in the hum an bod y du rin g rou tin e op era tion s is that o f in ­halation. The inhaled radioactive p a rticles may be tran sferred intothe circu la tion and deposited in a c r itic a l organ . They m ay in ju red ire ctly the r e s p ira to ry su rfa ce s o f the lungs o r be ab sorb ed bybronchial lymph nodes. The depth of penetration into the respiratorysystem depends on p a rticle s iz e . S m all p a rticle s fr e e ly enter thelo w e r p ortion s o f the lungs; la rg e p a rticle s a re d ep osited m ainlyin the upper re s p ir a to r y tra ct and a re ea sily c le a r e d .Usually p a rticles are heterogeneous in size. V ery often radioactivem aterial is attached to p a rticles of inert m aterial.The fu rth er fate o f inhaled p a rticle s depends upon th eir solu ­bility in body fluids. It determ ines to a large extent their depositionand subsequent excretion (see F ig. 15).1.4. 2. 3. A bsorption through the skin ^The intact skin absorbs v ery little radioactive m aterial. Tritium ,h ow ever, and som e oth ers can be so ab sorb ed . The p erm ea b ilityo f skin w hich has been in ju red even by su rfa ce a b ra sion s is v e rycon sid era b ly in cre a se d . Wounds p erm it open entry of ra d ioa ctiv em a teria l. The p re s e n ce o f org a n ic solven ts on the su rfa ce o f theskin a ls o a c c e le r a t e s the p e n e tra tio n o f r a d io a c t iv e m a t e r ia ls .When la rge quantities of rad ioactive m aterial com es in contactwith the skin, e.g. during an industrial accident, the skin absorptionshould be taken into consideration.45'


This publication is no longer validPlease see http://www.ns-iaea.org/standards/100(HLUQ_ 30Jl liUiH C Na P S K Ca Sr Y Zr Nb I Cs Ba La Ce Pr Ra PuFIG. 15. Distribution o f radioisotopes in experimental animals after inhalation [1 1 ].□ whole body ■ bones S thyroid B muscles •63 fat 0 skin1.4.3. Deposition of absorbed radionuclidesThe effects of absorbed ra d ioactiv e m aterial d iffe r fro m thoseof external radiation as they are m ostly unevenly distributed withinthe body and their p resen ce constitutes a continuous sou rce of ra d i­ation. When the ra d ioa ctiv e m a teria l fo rm s a 'point s o u r c e 1, thecells in the vicinity receiv e a substantially higher dose than the cellswhich are situated fa r aw ay. In such ca s e s it is v e r y d ifficu lt todeterm ine the real radiation d ose. F or this reason also the use of theRBE factor m eets with many difficu lties.The distribu tion of radioa ctive substances entering the body isinfluenced by th eir ch em ica l ch a ra cte ristics and by th eir ch e m ica lin teraction s with body constituents; they con cen trate in p a rticu la rorgans which are designated 'c r it ic a l org a n s'. The ICRP has c a l­culated for different c r itica l organs 'm axim um p erm issib le con cen ­46


This publication is no longer validPlease see http://www.ns-iaea.org/standards/tration s’ fo r about 250 radionuclides based on radioactive ch aracteristicsof these nuclides and their m etabolism in the 'standard man'(see part 3).The deposition o f internal em itters has been extensively studiedon experim ental anim als and also in man whenever adequate data hasbeen available.A lkaline earths like strontium and radium a re m etabolized likeca lciu m . T hey a re d eposited and retained in the bon es. T hey a renot even ly d istribu ted , but m ay fo r m sm a ll fo c i o f unusually highlo c a l con cen tra tion .The tox icity o f radium fo r man is quite w ell establish ed and ithas been used fo r estim ating the potential toxicity of other osteotropicn u clides. The sym ptom s o f radium poisoning appear 20 - 30 yea rsafter exposure to radium . An individual having 0.1 ng 226Ra 30 yearsa fter a sin gle exp osu re m ust have absorbed m uch m o re radiumin itia lly .S trontium -90 fo rm s a part of the b iosp h ere and it follow s c a l­cium in ca lciu m -ric h food s, esp ecia lly m ilk . It is deposited intensively in the bones of infants, together with ca lciu m . A fter then uclear tests great quantities o f stron tiu m -90 w ere introduced intothe food -ch ain s and as a resu lt a con sid era b le in crea se in the ratio90S r /C a has been o b serv e d . A s dem on strated in F ig . 16, this in ­c r e a s e is g reat, e sp e cia lly in infants.AGE (yr)FIG. 16. Age distribution o f 90Sr/Ca ratio in human bones [ 7 ],O 1961 ■ 196247


This publication is no longer validPlease see http://www.ns-iaea.org/standards/On the other hand ca esiu m -1 3 7 , produ ced a lso by the n u cleartests, is m o re u n iform ly distribu ted in the body, the la rg e st part(about 60%) being deposited in m u scles and the rest in v is c e r a l o r ­gans, brain, blood, bones and teeth in that o rd e r.Iodine-131 is se lectiv ely deposited in the thyroid. A fter inhalationabout 15% is retained and 20% after ingestion. R adioactive iodineis a ls o d ep osited to a slig h t d e g r e e in m u s c le s , b on es and sk in .Iodin e-131 m ay be a hazard if its con cen tration in the th yroidgland is in cre a sed . A fter the W in d scale r e a c to r incident in 1957la rg e quantities of 131I escaped to the environm ent. The ch ild 'sthyroid is very sen sitive to irradiation . A dose of 200 rads of X -ra y sto the neck may induce carcin om a in the thyroid in about 3% of ca ses.As the milk after W indscale incident contained m ore than 1 /jCi 1311/litre(this correspon ds to an integrated dose of about 130 rads to the ch ild 'sthyroid) much o f the m ilk produced in the area had to be d isca rd edfo r six w eeks.R adioactive ca rbon , im portant beca u se o f its long h a lf-life(5700 y ea rs), is produced by the in teraction of neutrons with atm o­sp h eric nitrogen. It is in corp ora ted in many im portant vital c o m ­pounds where it can act as a sou rce of soft beta radiation or ch em i­cally through its transm utation to nitrogen.Polonium and plutonium belong to the m ost toxic alpha sou rces.The toxicity of 210Po is about 120 tim es g rea ter than that o f 226Ra.P olon iu m is distribu ted quite u n iform ly in the body, plutonium iscon cen trated predom in an tly in bon es, liv e r and o v a ry .1.4.4. Elimination o f radionuclidesR adioactive nuclides introduced into the body may be elim inatedby kidneys, lungs through the gut, by sweat glands etc. Substancesd issolv ed in body fluids a re ex creted predom inantly in u rin e. Thebow els elim inate isotop es which have been partly absorbed and alsothose which have passed without absorption through the digestive tractowing to th eir low solu bility. R adioelem en ts a re m ost rea d ily r e ­m oved fro m n erve and m u scle tissu e, m uch m ore slow ly fro m thekidneys and the c e lls o f the reticu lo-en d oth elia l system , and m ostslow ly o f all fro m the b on es. In the lym ph nodes ra d ioa ctiv e e le ­m ents a re retained fo r a com p aratively long p eriod . G aseous is o ­top es such as radon a re elim in ated m ost ra p id ly by the lu n gs.The elim ination rate is governed by the age of the organism , byits p h y siolog ical condition, nature of the radionuclide, by the quantityof isotopes in the whole body and other fa ctors. The elim ination4 8


This publication is no longer validPlease see http://www.ns-iaea.org/standards/of caesiu m -137 by m ice is dem onstrated in F ig. 17. It must be r e ­m em bered that the exponential relation is not com m on. In m ost casesthe elim ination curve has a com plex ch aracter and only in restrictedtim e -in te rv a ls has an exponential ch a ra cte r. The b io lo g ic a l h a lflifeT b m ay be d ir e c tly d eterm in ed fro m the graph in F ig .,17 (T =7 d a y s). It can be e x p re sse d as fo llo w s:= ln_2 = 0. 693b " X b “ Xbw here Ab is constant of b io lo g ica l elim in ation . If Ar is the d isin teg ­ration constant o f the ra d ioisoto p e, then the e ffe ctiv e constant Xeff isX e ff = X r + X band T eff , the e ffe ctiv e h a lf-life , isIn 2 _ 0.693 _ Th Treff‘ X+Xb Xt + X„ T b + T r 'w h ere Tr is the ra d io lo g ica l h a lf-life .4 9


This publication is no longer validPlease see http://www.ns-iaea.org/standards/The e ffe ctiv e h a lf-life is the p ro p e r m eans of ex p re ssin g theduration of contam ination by a certain radion u clide. The p h ysicalh a lf-life fo r caesiu m -137 is 33 y ea rs, and this circu m stance mightseem to designate caesiu m -1 3 7 as a dangerous radion u clide. Butsin ce it is v e ry rapidly excreted , its effectiv e h a lf-life is only25 days and th e r e fo r e it is c la s s ifie d as m o d e ra te ly d a n g e rou s .E ffective h a lf-life is only one fa ctor for the evaluation of m aximump erm issible dose. Among others, the critica l organ is of prim eim p orta n ce. H ere the con cen tration o f the radion u clide, the rateof elim ination, the im portance of the organ or tissue fo r the functiono f the organ ism , its ra d iosen sitiv ity etc. a re fa ctors which shouldbe c o n s id e re d .1.4.5. Factors modifying the absorption and elimination ofradionuclidesThe therapy for radioactive poisoning is b asically a ph arm acolog ica l problem which is in many resp ects sim ila r to acute p oison ­ing with som e m etals. It su ffices here to mention only som e generalp rin cip les of decontam ination. It is vital to lim it the deposit ofradioactive substances in the cr itic a l organs by rapid and p rop erlyd irected m easu res of a ssistan ce.In ca ses w h ere a ra d ioa ctiv e su bstan ce has a lrea d y been in ­corp ora ted in the organ ism , it is even m ore n ece ssa ry than in theca se o f fir s t aid to take into accou nt the nature o f the ra d io a ctiv em a te ria l absorbed and to treat the patient a cco rd in g ly .The aim of internal decontam ination is to a ccelera te the e lim ­ination of ra d ioactiv e m a terial at the stage o f acute o r ch ron icpoisoning, as the case may be. It is to be rem em bered that the greatm ajority of radioactive elem ents, when once absorbed, are elim in ­ated only gradually by natural p r o c e s s e s . It is, for example, p ra ctica l­ly im p o ssib le to rem ov e radium from the body once se v e ra l w eekshave elapsed follow in g in gestion . A ll attem pts to brin g about as p e e d ie r elim in ation o f an absorb ed ra d ioa ctiv e m a teria l m ay bereg a rd ed as based on the follow in g p rin cip le s :(1) Taking advantage of the corresp on d en ce of the m etabolismo f the radioelem en t with a related elem ent in the patient (e.g.stron tium and ca lciu m );(2) Taking advantage of the discrim ination made by the organismbetw een a ra d ioa ctiv e elem ent and a c h e m ica lly rela ted but non ­ra d io a ctiv e elem ent; and5 0


This publication is no longer validPlease see http://www.ns-iaea.org/standards/(3) The u tiliza tion o f c o m p le x -fo r m in g su b sta n ce s.EDTA is rela tiv ely to x ic and in sm a ll d oses induces h y p o ca l-caem ia. It is th erefore adm inistered in the form of CaEDTA whichis not m etabolized and is rapid ly elim inated in the urin e, w h ereasthe ca lciu m is to a certa in d e g re e exchanged fo r oth er m e ta b o licion s. F o r som e elem ents like plutonium, thorium , yttrium and ther a r e earth s the ch elatin g agent d ie th y le n e -tria m in e -p e n to a ce ta te(D TPA) has proved su p erior to the CaEDTA. P rolonged treatm entwith DTPA effectiv ely rem oves part of deposited plutonium.1.4.6. Effects o f absorbed radionuclidesThe radiotoxic effect of radioisotopes on the organism is a co m ­plex function which depends on a variety o f physical fa ctors, one ofthe m ost im portant of which is the physical h a lf-life of, and thestrength and type o f radiation emitted by, the isotope. The chem icaltoxicity o f the isotop e is a lso som etim es im portant. F o r uraniumits toxicity as an elem ent must be considered in relation to its radioactivep rop erties. With regard to the organism , too, a whole serieso f b io lo g ica l fa cto rs are in volved, such as the m ode of entry o f thera d ioa ctiv e m a teria l, the site o f its d ep osition and the rate o f itselim ination. A nother im portant fa cto r is the age and the assum edrem aining life -sp a n o f the org a n ism .E a rly effectsIn experim ental anim als early effects have been observed afteradm inistration o f lethal d oses of ra d ioactive m a teria ls. They appeared7-10 days after exposure and included m ostly haematopoieticsym ptom s of acute radiation d isea se. There have been observationso f early effects in man after accidental intake of radioactive m aterial(e.g. the acciden tal exposu re of 103 lu m in ou s-dial painters to 90Srinvolved urinary excretion and early haem atological effects as w e ll).Late effectsL ong-term effects follow ing ingestion of sm all amounts of internalem itters m ay be a seriou s p rob lem . The in ciden ce of lungca n cer am ong S chneeberg and Jachym ov uranium m in ers is at least50% h igher than that in the g en era l population. O ther data fro mC olorado Plateau and the St. L aw rence region also strongly suggest51


This publication is no longer validPlease see http://www.ns-iaea.org/standards/the p ossib le induction of lung ca n cer by radon and its daughtersp resen t in the m in es. The average latent p eriod fo r the inductionof lung ca n ce r is ~ 17 y e a rs and a cco rd in g to approxim ate c a lc u ­la tio n s the d o s e d e liv e r e d d u rin g th is tim e is h u n d red s o f r a d s .Radium is a bon e-seek in g elem ent and its deposition in them ineral part of the bone induces bone m alignancy (osteogen ic s a r ­com as and carcin om as of the paranasal sinuses and m a stoid s). Noclin ica lly sign ifican t sign s have been o b se rv e d with re sid u a l bodyburdens of < 0 .5 juCi Ra. With in crea sin g quantity of in corp oratedm aterial the in ciden ce of these tum ours in cre a ses.E xperim ents with anim als have elucidated to a certain d egreethe m echanism of the dam age caused by b on e-seek in g (osteotrop ic)elem ents. Bone dam age appears in two fo rm s. F irst, bone is injuredthrough d estru ction of blood v e s s e ls and by d ire ct a ction onthe osteocytes. Secondly, the radiation of the internal em itter causesabnorm al activity in osteogen ic connective tissue, leading to m arkedterm inal fib rosis . With sm all d oses there is a p ossibility of rep airin bon e. It is in terestin g that the form a tion o f tu m ou rs m u st notn e c e s s a r ily be p re ce d e d by s e v e r e dam age to the b on e.The in cid en ce o f tum ours in experim en ta l an im als in c r e a s e swith accum ulated d ose and at h igher d ose ra tes. D ose ra tes varyw id ely in exp erim en ts with in tern al e m itte rs. T his com p lica te s ,am ong other fa ctors, the determ ination of the c o r r e c t relation sh ipbetw een tum our induction and absorbed d ose.The fa r g rea ter induction of bone tum ours in experim en ta lanim als overshadow s the in ciden ce of other types of tum ours, e.g.of leukaem ia. This d isea se has been rep orted in radium patients,but only in those who w ere exposed at the sam e tim e to high d oseso f external gam m a radiation.52


This publication is no longer validPlease see http://www.ns-iaea.org/standards/2. RAD IOLOGICAL HAZARDSF rom the p6int of view of m onitoring and protection , a d istin c­tion m ust be m ade, a ccord in g to the way in which radiation en tersthe organism , betw een:(a) E xtern al irradiation fro m a d istance, and(b) R adioactive contam ination.E xternal irradiation originates from sou rces at a distance fromthe body which em it radiations o f such nature and energy as to reachit, X - and gamma rays, beta p a rticles, n eu tron s.-R adioactive contam ination o ccu rs when radioactive substancesare brought into contact with the body, either su p erficially (externalor skin contam ination) o r within the body (internal contam inations).2.1. EXPOSURE TO NATURAL RADIATIONB efore d iscu ssin g occupational exposu re, we should r e ca ll thatw o rk e rs, like any oth er p e rso n s, a re su b ject to natural radiation .Studies devoted to natural radioactivity have thrown light on itso rig in s , the a v era g e d ose resu ltin g in the m ost d en sely inhabitedp a rts o f the w orld and its p e rio d ic flu ctu ation s.C osm ic rays originate in in terstella r sp aces and d eliv er to thehuman body a dose estim ated at 30 m illirem s a year in the P arisianarea.The soil and building m aterials around us contain tra ces of uraniumand th oriu m , som e daughter p rod u cts o f w h ich em it gam m arays; the resulting dose varies greatly from place to place. Amongthe daughter products of uranium, radon is a gas which diffuses intothe a ir; it cau ses external irradiation because of its active deposit,in which som e o f its daughter p rod u cts are gam m a e m itte rs. It isalso inhaled, thus bringing about internal (alpha, beta, gamma) con ­tam ination o f the body, which is accentuated by the in gestion o f tra ceso f uranium con tain ed in w ater. T he d ose resu ltin g fr o m this en ­viron m en ta l ex p osu re is estim ated at 50 m illir e m s a y e a r in theP a risia n a rea.A ccount m ust a lso be taken o f the natural ra d ion u clid es whichen ter the com p osition o f the bod y and a re regu la rly ren ew ed by afo od -ch a in : p ota ssiu m -4 0 and ca rb o n -1 4 d e liv e r an a vera ge doseto the body o f som e 20 m illire m s a y e a r.53


This publication is no longer validPlease see http://www.ns-iaea.org/standards/A s a w hole then natural ra d ioa ctiv ity re su lts in an ex p osu rew hich a v era ges about 100 m illir e m s a y e a r in sedim entary a re a s.C osm ic radiation in crea ses with altitude, being three tim es asm uch at 3000 m etres as at sea level. T here is little variation withlatitude.The dose d eliv ered to the body by the natural radion u clid es itcontains does not vary as the body content o f and 14C is stable.On the other hand the abundance of radioactivity in the soil may resultin wide variation s in extern al d ose. In som e parts of the w orld, inB ra zil o r India fo r exam ple, the corresp on d in g dose is as m uch as1500 m illire m s a y e a r. T hese a re excep tion al c a s e s , but in v e rym any c a s e s the d ose is betw een 150 and 400 m illir e m s a y e a r,e sp e cia lly fo r populations livin g in g ra n itic d is tricts w h ere h ou sesa re built with m a teria ls drawn fro m the s o il.2.2. M EDICAL EXPOSU RE2. 2. 1. S ources o f m edical exposureThe radiation sou rces used for m edical purposes may be cla s s i­fied as extern al s o u rce s o r internal s o u rce s a cco rd in g to w hetherthey a re applied outside o r in side the human body.2. 2. 1. 1. E xtern al s o u rcesE xtern al s o u r c e s in clude ra d ia tio n -p ro d u cin g equipm ent andseale d ra d ion u clid e s o u r c e s .2. 2. 1. 1. 1. Radiation-producing equipm ent. The radiation-producingequipment used in m edical radiology is, in practice, all based on thesam e p rin cip le . A cce le ra te d e le ctro n s a re p ro je cte d on a ta rgeto r em itted fro m the apparatus. In the fo r m e r ca s e a bea m o f X -ra y s is g en erated , in the la tter a bea m o f e le c tr o n s .(1) X -ra y equipment com p rises three separate parts: (a) an e le c ­tron generator; (b) an acceleratin g d evice; and (c) a target.E lectron g en era tors a re b a sed on the th e r m o -io n ic e m issio n .A m etal heated to a high tem perature em its electron s which can besca tte re d fro m the m etal if they a re su b jected to e le c t r ic fo r c e s .54


This publication is no longer validPlease see http://www.ns-iaea.org/standards/E lectron a ccelera tion m ay be obtained either by e le c tric or bym agn etic fo r c e s . E le c tr ic a c c e le r a tio n o f e le c tr o n s is u sed inc la s s ic a l X -r a y equipm ent, fo r ra d io d ia g n o stic and con v en tion a lradiotherapy pu rp oses. The e le c tr ic potential d ifferen ces used arein the range of 50 000 to 400 000 V.E lectron s can a lso be a cce le ra te d by m eans o f p ow erfu l m agnetic fo r c e s . Equipm ent of the b etatron type p rod u ces a c ir c u la ra cceleration of the electrons situated in a magnetic field the lines offo rce o f which are perpendicular to the plane on which the electron sm ove.The a cce le ra te d electron s are p ro je cte d on a target made o f ap articularly heat-resistant m etal. The interaction between the e le c ­tron radiation and the ta rget atom s g iv e s r is e to X -r a d ia tio n andit is this X -ra d ia tio n which is used fo r the p u rp ose o f m ed ica lra d iolog y .The X -r a y beam thus obtained is ch a ra cte riz e d p r im a r ily byits quantity, quality and d ire ctio n .(2) E lectron radiation gen erators are based on the sam e prin ciplesas the foregoin g; they com p rise two parts only, an ele ctro n gen e­ra to r and an electron a c c e le r a to r . The electron beam , instead ofim pinging on a target, is used as it co m e s from the apparatus.A m ong the g en era tors studied above, on ly th ose capable o f givingelectron s su fficien t a ccelera tion a re used, electron radiation beingo f no in terest fo r th erapeu tic p u rp o se s excep t when the e le ctro nenergy is high enough to enter fa irly deeply into human tissu e. G e­n era tors used fo r this purpose a re m ainly lin ear a c c e le r a to r s andbetatron s. H ere again, the e le ctron beam is ch a ra cte riz e d by itsquantity, quality and d irection .2. 2. 1.1. 2. Sealed radionuclide s o u r c e s . Sealed radionuclide sou r­ces are used in m edical radiology for external irradiation when theyem it g am m a o r b eta ra d ia tion o f su ita b le in ten sity and q u a lity .(1) G a m m a -ra y s o u rce s a re m ainly p rovid ed by th ree ra d io ­nuclides, radium -226, cobalt-60 and c a e s iu m -137. The ch a ra cteristicso f such s o u rce s a re dependent on the h a lf-life of the ra d ionu clid e, tne radiation output p e r unit o f a ctiv ity and the radiationen ergy. The h a lf-liv e s o f 226Ra, 60Co and 137Cs a re 1600, 5, and30 y ea rs re sp e ctiv e ly . The output of a o n e -cu rie sou rce at onem etre per hour is 0.84 R for radium -226; 1.35 R for cobalt-60; and55


This publication is no longer validPlease see http://www.ns-iaea.org/standards/0.39 R for c a e s iu m -137. The gam m a-ray en ergies are 0.2-2.2 meVfor radium -226; 1.17-1.33 m eV for cob a lt-6 0 ; and 0.662 m eV forcaesiu m -137.(2) B eta-ray sou rces are used for su p erficial external irra d ia ­tion. The sou rces m ainly used are 32P or 90Sr/9°Y sou rces. Theya re ch a ra cte riz e d m ainly by the am ount o f m a teria l p re sen t, thequality of the beta radiation em itted and the maximum energy of thebeta radiation. This is 1.710 meV for p h osphoru s-32 and 0.544 meVfor stron tium -90/yttriu m -90. The beta p articles thus emitted filterless well into the organism , and the range isO. 7cm for phosphorus-32and 0.9 cm for stron tium -90/yttriu m -90.2. 2. 1.2. Internal sou rcesA ll internal radiation sou rces are radionuclide sou rces, eithersealed or unsealed.Sealed sou rces are designed to prevent the radioactive m aterialfrom being diffused into the body and m etabolized. The so u rce s inquestion a re a p p lica to rs, n eed les o r th read containing the r a d io ­a ctive m a teria l within a tight e n clo su re . The ra d io isoto p e s u sedare gamma or beta plus gamma em itters but the protective enclosurew hich preven ts ra d ioa ctiv e lo s s a lso acts as a filte r and only letsout the gamma radiation. The sm allest sou rces (in term s of length)are m ade of radiu m -226, radon -222, cob a lt-6 0 , gold -1 9 8 and tantalum -182. T h eir ch a ra cte ris tics a re dependent on the amount ofradionuclide they contain, the en ergy of the gam m a radiation em itted,the h a lf-life of the radion u clide and the g e o m e trica l shape o fthe so u rce . T here are s o u rce s containing v e ry s h o rt-liv e d ra d io ­n u clid es (222Ra, 198Au) which can be left within the body, w h ereasthe oth ers must be withdrawn.Unsealed sou rces are so made that once introduced into the bodythey diffuse and can particip ate in the m etabolic p r o c e s s . T h e r e ­fo r e only ra d ion u clid es with su itable p h y sica l, p h y s ic o -c h e m ic a land ch em ical ch a ra cteristics should be used. F or exam ple, use ism ade o f 198Au or ch rom iu m phosphate ra d io co llo id s, as w ell as ofm a teria ls in ionic fo rm with known m etabolism (32P, 1311). T hesesou rces are ch aracterized by the amount of radionuclide introduced,the nature and en ergy o f the beta o r gam m a radiation em itted andthe h a lf-life o f the radion u clide con cern ed.56


This publication is no longer validPlease see http://www.ns-iaea.org/standards/2. 2. 2. F orm s o f m edical exp osu reA ccord in g to th eir ch a ra cte ristics, the foregoing sou rces maybeused in m e d ica l ra d iolog y fo r eith e r d ia gn ostic o r th erapeu ticp u rp oses.2. 2. 2. 1. D iagn ostic u sesF or diagnostic pu rp oses X -r a y or radionuclide s o u rce s can beused.X -r a y s a re by fa r the m ost w idely u sed. The apparatus e m ­p loyed fo r the p u rp ose is the con ven tion al type o f g e n e ra to r withvoltage betw een 50 and 100 kV.The use of radionuclides for diagnostic purposes is in the mainlim ited to unsealed s o u rce s , w hose d istribu tion in the body can beu sed fo r a n a to m ica l (sca n n in g) o r fu n ction a l (tu rn o v e r) stu d ie s.2. 2. 2. 2. T h e ra p e u tic u sesThe foregoin g sou rces have a great variety o f therapeutic u seswhich can be divided into teletherapy (or rem ote radiotherapy), su p erficial therapy and in terstitial therapy.The m ain s o u rce s u sed in teleth erapy a re h ig h -en erg y X -r a yapparatus (in the 200-kV range — Van de G raaff m a ch in es, lin ea ra c c e le r a to r s and betatron s), ele ctro n radiation g en era tors (lin eara c c e le r a t o r s and b eta tron s) and g a m m a -ra y g e n e ra to rs (radium ,cob a lt o r ca e siu m units).F or s u p e rficia l radioth erapy the follow in g types o f apparatuscan be u sed : v e r y -lo w -e n e r g y X -r a y apparatu s; seale d gam m as o u r c e s (radiu m -226 and c o b a lt-6 0 a p p lica to rs); and sea led betaso u rce s (phosphorus-3 2 and stro n tiu m -9 0 /y ttriu m -9 0 a p p lica tors).In terstitia l radioth era p y can u s e : seale d gam m a s o u r c e s(radiu m -226, co b a lt-6 0 o r g o ld - 198); and u n s e a le d 's o u rce s (gold-198, p h osp h oru s-32 o r iod in e-131).2. 2. 3. Results o f medical exposureIn con sid erin g the resu lts o f m e d ica l e x p osu re, a d istin ctionshould be m ade betw een the irra d ia tion o f sta ff engaged in r a d io ­lo g ica l exam inations and treatm ent, and the irradiation of patients.A s the irradiation o f staff is dealt with in the next section , only i r ­57


This publication is no longer validPlease see http://www.ns-iaea.org/standards/radiation o f the public for diagnostic or therapeutic purposes shouldbe taken into account.M ed ica l irra d ia tion o f the pu blic in alm ost a ll c a s e s in v olv esp a rtia l irradiation o f the body. T h ere a re only a few excep tion a lkinds of treatm ent, including certain types of treatm ent with ra d ioisotopes which a re distribu ted g en era lly (such as p h osp h oru s-3 2 ),which involve w hole-body exposure. In all other cases the exposurem ust be view ed with re g a rd to the ra d io se n sitiv ity o f the tis s u e s .On this basis a m ajor distinction can be drawn between irradiation ofthe bone m arrow (for som atic effects) and irradiation o f the gonads(for genetic e ffe cts ). It should be born e in m ind that not a ll typeso f ra d io lo g ica l exam ination and treatm en t a re equ ally im p ortan t.T h ose involving the use o f unsealed radion u clide s o u rce s a re onlya sm a ll percen tage o f those which em p loy radiation gen era tors o rsealed radionuclide sou rces. M oreover, ca ses of radiotherapy r e ­p resen t only a sm a ll p ercen ta ge o f ra d iod ia gn ostic exam in a tion s.Finally, certain examinations contribute m ore especially to irra d iationo f the bone m arrow o r the gonads. F or exam ple, examinationso f the p e lv is and the lo w e r part o f the g a s tro -in te s tin a l tra ct a reresp on sible for the greater part of irradiation of the gonads.2.3. O CCU PATIO N AL EXPOSURE2.3.1. A tom ic energyTo study these hazards it is easiest to follow the route of radionuclidesin the atom ic industry.(1) The p ro ce ssin g o f fuels to be used in re a cto rs includes orem ining, ore enrichm ent and final p ro ce ssin g of the fuel.Uranium mines are always subject to regular hazards. Gammaex p osu re is u su ally low . T h ere is a r is k o f ex tern a l irra d ia tio n ,but it is of lim ited extent and only encountered in exceptional ca seswhen concentrations a re o f the o rd e r o f 1% and w here there is su f­ficient ore in the working gallery. However, the risk of the air becom ingcontam inated by radon and daughters o r radioactive dusts and a e ro so lsis con sid era b le. P rim a ry radioactive dusts (uranium p a rticle s ) areto be distinguished from secon d ary radioactive dusts (inert dust onwhich solid daughter products of radon are deposited). Radon a lsod issolv es in a e ro so ls resulting from w ork with water sprays; thesea e r o s o ls fo rm a m ist in the m ine. The a tm osp h eric r is k is tw o-58


This publication is no longer validPlease see http://www.ns-iaea.org/standards/fo ld : it can en tail skin con tam ination and in tern al con tam in ationfollow ing inhalation. The pollution o f mine w aters is only a se co n ­dary danger.Ore m illing plants are subject to the sam e hazards from gammaradiation and a ir contam ination. W ork ers handling o re at 20% areex p osed to sign ifican t quantities o f gam m a radiation . A ir con ta ­m ination re su lts from the radon given o ff and the dust sca tte re ddu rin g cru sh in g and grin din g o p e ra tio n s.In plants p roce s s in g m eta llic uranium o r thorium a ll daughterp rod u cts o f uranium o r thorium which a re contained in the o re areseparated and treated as w aste. This con siderably reduces the risko f irradiation , but contam ination risk s rem ain , a risin g e sp e cia llyfro m w ork on oxid es and flu orid es.In isotope separation plants there are risk s o f acciden tal contaminationfrom gases o r dust.(2) At n u clear re a c to r s the p rim a ry radiation hazards to w ork ersa re either by exp osu re to gam m a rays o r neutrons leaking d irectlyfro m the r e a c to r through the channels when these a re open o r e x ­p osu re to beta o r gam m a radiation fro m the activated m a teria ltaken out o f the r e a c to r .During n orm al operation the ris k o f ra d ioactive contam inationis alm ost en tirely confined to the coolin g fluid, slight leakage beingalw ays a p o ssib ility in clo s e d c ir c u its . M o re o v e r, such incidentsas a bu rst pipe a re alw ays p o s s ib le .The m ost se rio u s a ccid en t re su lts fro m the co n s id e ra b le in ­c re a s e in tem perature which takes p la ce when there is in su fficien tcoolin g inside the r e a c to r . Dusts fro m p rim a ry (U) o r secon d ary(Pu) fuel and gaseous fission products w ill then be released throughthe bursting o f the fuel cladding and may entail seriou s contam inationof the a ir.(3) W orkers in ch em ical or m etallurgical plants which rep rocessm aterial from re a cto rs o r b y-p rod u cts m ay be subjected to sig n ificantirradiation.;For instance when Pu is ex tra cted , fis s io n p rod u cts a re to befound togeth er with the fuel and storage is req u ired to allow sh ortlivedfissio n p rod u cts to d ecay. P e rson n e l engaged in p r o c e s s in gch em istry are su bjected to beta irradiation from the la rge amountso f 32P and 90Sr they have to handle.In m etallurgical plants, only the processin g of som e special m a­te r ia ls such as cob a lt and yttriu m en tails the r is k o f e x p o su re togamma or beta radiation. In the cou rse of routine operation of theseplants there is a risk of two types of contamination:59


This publication is no longer validPlease see http://www.ns-iaea.org/standards/(a) Superficial contam ination o f the skin, m ainly due to liquids;and(b) A ir contam ination. This is in fact the ch ief hazard in m illshandling uranium and plutonium m etal. T h ese prod u cts w hich a realpha em itters rank am ongst the m ost dangerous that ex ist andsp e cia l m easu res m ust be taken to con tro l a ir contam ination.A ccid en ts m ay a lso o ccu r: the bu rstin g o f a tank o r pipe in ach em ica l extraction fa cility m ay resu lt in exceed in gly se rio u s a ircontamination owing to the quantity o f radioactive m aterials handled.In m eta llu rgical plants fir e s a re frequent as m eta llic uraniumand plutonium becom e v e ry easily oxid ized. T his may give ris e toatm osph eric pollution, subjecting nearby w ork ers to seriou s a c c i­dental hazards.2. 3. 2. Industrial use o f ionizing radiation2. 3. 2. 1. Use o f radionuclide sou rcesNowadays m ost sou rces, whether used in m edicine, agriculture,industry o r scien tific resea rch , a re m an-m ade and have a short orm edium h a lf-life Usually they are beta or gam m a em itters, le s sdangerous in the event of contam ination than alpha em itters. F romboth the qualitative and quantitative points of view the risk s are muchsm a lle r than in n u clear fa cilitie s . Tw o types o f u se can bedistinguished:(1) Use o f sealed sou rces (gam m a radiography), which entailsonly risk s of exposure to gamma or som etim es beta radiation. Thereis the p ossib ility of the shielding being acciden tally dam aged in theevent o f fire or a fall;(2) Use o f unsealed so u rce s. The handling o f either pow dered,liqu id o r gaseou s ra d ioa ctiv e m a te ria ls m ay in volve a r is k o f e x ­tern a l irradiation and a th reefold ris k o f contam ination:(a) S uperficial contamination o f the skin o r clothing or contam i­nation of p rem ises(b) A ir con tam ination , resu ltin g in in tern al con tam ination ofthe individual through inhalation when v o la tile su b sta n cesa re form ed(c) Internal con tam ination by the liq u id s th e m se lv e s (e.g. byaccid en ta l intake).P o ssib le accid en ts a re ru ptu res, sp illin g o f la rg e am ounts o ru n con trolled d isp osa l. In the event o f fir e , a tm osp h eric p ollutionis m o re seriou s than in the p rev iou s ca se.6 0


This publication is no longer validPlease see http://www.ns-iaea.org/standards/One o f the m ost striking exam ples in this connection is the useo f unsealed so u rce s fo r painting lum inous d ials, etc.2. 3. 2. 2. Use o f radiation gen era torsR a d ia tion -g en eratin g apparatus (X -r a y tubes and p a r tic le a c ­ce le ra to rs such as Van de G raaff m ach in es, betatrons and c o s m o -tron s) may involve w ork ers in exposure to: the direct particle beam(instances of occupational cataracts resulting from a cy clotron p a r­ticle beam are w ell known); o r the secon d a ry radiation em itted bythe ta rg ets, u su ally X -r a y s o r neutron b ea m s. The dan gers varya ccord in g to the m ode of operation o f the apparatus (the neutron e -m ission o c c u r s in the Van de G raaff a c ce le ra to r at a v ery highvoltage), and a lso a ccord in g to the target m aterial.Som e o f this apparatus is o cca sio n a lly u sed to p rod u ce ra d io ­nuclides, so som e contamination hazards a re a lso encountered. Howev er, the main hazard by far is external irradiation.2. 3. 3. Transport o f radioactive m aterialsT ra n sp o rte d m a te ria l can be d iv id ed into: ra d io a ctiv e o r e s ,typified by th eir v e ry g rea t w eight and th e ir low s p e c ific a ctiv ity ;irradiated fu els, typified by th eir sm all bulk and v e ry high sp e cificactivity; and activation and fissio n p rod u cts used as s o u rce s , alsotypified by th eir sm all bulk and high sp e cific activity.T h e re a re tw o kinds o f h azard a ris in g fr o m the tra n sp ort o fth ese m a te ria ls by roa d , r a il, ship o r a ir , e tc . : the r is k o f e x ­tern al irradiation when the radioa ctive m aterials are gam m a em itters o r en erg etic beta em itters; and the risk o f ra d ioactiv e con taminationonly in ca se of damage to the container or package, due forin stan ce to a tr a ffic a ccid en t. The s e r io u s n e s s o f the a ccid e n ta lh aza rd s depends on the nature and the am ount o f the m a te ria lstra n sp orted .2.4. CONCLUSIONSIn sum m ing up the re su lts o f occu p a tion a l e x p o su re h a za rd s,tw o types o f circu m s ta n c e s a re to be distin guish ed.The fir s t type co rre s p o n d s to n orm a l w ork ing co n d itio n s. Itentails the risk o f external irradiation o r radioactive contam ination61


This publication is no longer validPlease see http://www.ns-iaea.org/standards/accord in g to the ca ses con sid ered above. Such irradiation o r co n ­tam ination must be kept within lim its com p atib le with the r e c o m ­m endations o f the <strong>International</strong> C om m ission on R a d io lo g ica l P r o ­tection , and m ust th e r e fo r e in any ca s e be as low as p r a c tic a b le .It should be pointed out that a d m in istratively d ifferen t lim its m ayapply to w ork ers engaged in radiation w ork depending on the c o n ­ditions o f w ork (see section 3. 2. 1). F or exam ple, in a m etallu rgica l plant the team engaged in in d u stria l rad iogra p h y w ork u n d ercondition (i) while the other w ork ers w ork under condition (ii) (seesection 3. 2. 1).Other types o f occu p a tion a l exposu re m ay o c c u r in a bn orm alcircu m stances arising in connection with incidents or accidents. Thele v e ls reach ed in the event o f extern al irra d ia tion and ra d ioa ctiv econtamination may d iffer and may reach v ery high values. The lik e­lihood and the magnitude of exceptional exposures depend on the typeo f w ork p erform ed . It is not a se rio u s ris k in uranium m in es andis ra re ly significant in m ed ica l o r labora tory w ork but can b ecom eo f im portan ce fo r w ork done in the vicin ity o f n u clear r e a c to r s o rp a rticle a c c e le r a to r s .6 2


This publication is no longer validPlease see http://www.ns-iaea.org/standards/3. RADIATION PROTECTION STANDARDS3.1. G E N E RALBy 'radiation p rotection standards' is meant the whole systemo f lim its which can be set to extern al irradiation and internal co n ­tam in ation o f human bein gs so that no a p p re cia b le dam age shouldresu lt eith er fo r in dividuals o r fo r the population at la r g e .The standards recom m en d ed by the <strong>International</strong> C om m issionon R a d iolog ica l P ro te ctio n (IC R P) [13] and the IA E A B a sic <strong>Safety</strong>Standards fo r R adiation P ro te ctio n [14] in clude both lim its to theirra d ia tio n o f the w hole body o r v a rio u s o rg a n s - th ese fo r m theb a sic standards - and p ra ctica l lim its o r standards d eriv ed fro mthe fo r m e r and rela tin g to valu es d ir e c tly m e a su ra b le o r e a sy toestim ate, nam ely the d ose fro m exp osu re to the differen t types o fradiation and the m axim u m p e r m is s ib le con cen tra tion s o f r a d io ­n u clid es in w ater and a ir .3.1.1. B asic fa cto rs in the establishm ent o f radiationp rotection standardsT o d eterm in e what irra d ia tio n le v e ls can be re g a rd e d as a c ­ceptable account must be taken of : (a) the fact that man has alwaysbeen exposed to natural radioactivity; (b) the results o f experim entsm ade on an im a ls; and (c) fin a lly , data d e riv e d fr o m hum ano b se rv a tio n .3. 1.1.1. E xp osu re to natural ra d io a ctiv ityE xposure to natural radioactivity can be broken down as follow s:external irradiation : c o s m ic radiation, radiation presentin the s o il, radiation presen t in theatm osphereinternal contam ination: 40K; 14C; Rn; R a.T his am ounts to a total value o f 100 m r e m /y r fo r the gonads,about 100 for the bone m arrow and 130 for the osteocy tes. Thus theaverage annual amount o f natural radioactivity receiv ed by the individualis of the o rd e r o f 0.1 rem .63


This publication is no longer validPlease see http://www.ns-iaea.org/standards/It is also of in terest to know the fluctuations in these amounts,which m ay ea sily be as m uch as 200 to 300%.The amount o f natural radioactivity re ce iv e d is low fo r peopleliving in b rick houses, but the figure can be m ultiplied by two, three,four o r even five for people living in granite houses, owing to gammaem ission and the fact that granite d iffu ses radon into a ir and waterwhen uncoated. In som e p arts, such as India, this m u ltip licationfa cto r m ay be as high as 10, 12 o r 15. Thus it can be seen thatpopulations have developed in areas where they have been subjectedto ex p osu res ranging betw een 0. 1 and 1 rem p er y e a r without anyex tra ord in a ry e ffe cts appearin g.If the natural radiation dose is taken as 5 rem s o v e r a p eriodo f 30 years, one should not forget that actual doses received by individuals(ov er a 3 0 -y r period) v a ry betw een 3 and 50 rem s and thatm ost of the population living in sedim entary areas are exposed nearthe m inim um valu e, i.e. about 5 re m s o v e r 30 y e a r s . With suchd oses th ere is no risk of known th resh old e ffe cts and th is p erm itsus to estim ate an upper lim it fo r e ffe cts without a th resh old , e.g.in cid en ce o f m utations.3 .1 . 1. 2. A nim al exp erim en tsA second type of inform ation is provided by the extensive animalexperim en ts that have been m ade p r e c is e ly in o r d e r to e sta b lishca u sa l rela tion sh ip s betw een d ose and e ffe c t. T he lite ra tu reco v e rin g p ra ctica lly a ll th resh old e ffe cts is v e ry substantial, butit is thinner fo r effects without a threshold which, as has been seen,a re m uch m o re d ifficu lt to study. F ro m the gen etic point o f v iewfo r instance, the literatu re cov ers only som e sp ecies, som e m ic r o ­o rg a n ism s, som e in sects and, above a ll, the fru it fly D rosop h ila.R ecent litera tu re b ea rs on m ic e .A very large amount of inform ation is available which m akes itp ossib le on the one hand to com pare variou s sp ecies from the pointo f view of radiobiology and derive threshold values and on the otherto plot d o se-e ffe ct cu rves in the case o f genetic m utations.H ow ever, there are always uncertainties in extrapolating fromanimal to man, so that the above inform ation must be supplem entedby data concerning human observation s.3.1. 1. 3. Human observations. T hese observation s relate fir s tly to people exp osed fo r th era ­peutic pu rposes. In these ca ses it is no lon ger the ben eficial effects64


This publication is no longer validPlease see http://www.ns-iaea.org/standards/o f the radiation that are studied but the possible hazards. Radiationm a y , fo r in stan ce, resu lt in skin m o d ifica tio n s, lung tro u b le s ,s o m e tim e s the in cid en ce o f c a n c e r s , etc.Human ob serv a tio n s a lso co m e fro m p eop le who have u n d ergoneoccupational exposure. As far as radium is concerned they areo f the utm ost valu e, sin ce a w hole s e r ie s o f a u top sies have m adeit p o ssib le to d eterm in e the amount o f radium in side the body andthe varyin g d ose le v e ls and d eg rees o f dam age.T here is finally a third category of data, nam ely those relatingto atom bom b v ictim s, fo r whom causality relation sh ips have beenestablished, esp ecia lly fo r leukaem ia, skin and blood changes, etc.In the fie ld o f g en etics th ere a re p ra c tic a lly no data o f v alu e.As a human gen eration is o f the o r d e r o f 30 y e a rs and b eca u se o fthe relative novelty o f the su bject, it is cle a r that little inform ationis yet available.A whole a rra y of m ateria l is th erefore to hand. P h y sica l dataa re m ainly useful to d eterm in e what steps it is rea son a b le to takein the case of effects without a threshold. B iological data, fo r theirpart, throw a great deal of light on th resh old e ffe cts and so m akeit p o ssib le to d eterm in e the approp riate le v e ls .3.1.2. C ategories o f exp osureB efore turning to a p re cis e definition o f p e rm issib le le v e ls , itis desirable to indicate the general concepts underlying the standards,in particular those o f ca tegories of exposure and the m axim um p e r­m issib le d ose.A ll radiation can be cla ssifie d in two ca te g o rie s, natural background radiation and m an-m ade radiation.3.1. 2.1. Natural background radiationWhen standards are drawn up, whether for radiation w orkers orfo r the population at large, no account is taken o f natural radioactivity.T his g en eral tenet is o f the utm ost im p orta n ce. Naturalra d ioactivity can be used as a b a sis o f re fe re n ce in drawing upstandards, but it is not taken into account subsequently as it is subject to fluctuations and the ICRP has pointed out that it y a rie s co n ­sid era b ly fro m lo ca lity to lo ca lity . T h e re fo re the resu ltin g d osesto va riou s organs are not w ell known.65


This publication is no longer validPlease see http://www.ns-iaea.org/standards/"If m aximum p erm issib le lev els included background radiation,the allow able contribution from m an-m ade sou rces - which are theonly ones that can be controlled - would be uncertain and would haveto be different for different lo ca litie s. A ccordingly, doses resultingfrom natural background radiation are excluded from all m axim ump e rm issib le d oses recom m en d ed " by the IC RP.3.1. 2. 2. M an-m ade radiationIn the field o f m an -m ade radiation two types o f exposu re a renow distinguished, i.e. m ed ical and n on -m ed ica l. This distinctionis made partly because m edical sou rces o f radiation contribute s ig ­nificantly to the radiation exposure o f the population as a whole, andpartly becau se o f th eir sp ecia l a sp ect. In the field of m ed ica l e x ­posu re, it is obvious that any radiologica l examination o r treatm entis p e rfo rm e d fo r good re a so n s, i.e. b eca u se it is su p p osed to ben eeded. E ven so, duplication m ay happen ow ing to d e fe cts inadm in istrative organ ization , and abuses do o c c u r .R adiological exam ination o r treatm ent undertaken deliberatelyhas the sp ecia l ch a ra cteristic o f being designed to ensure the in d i­vidual's health. T h erefore, though it does to som e extent constitutea hazard, it cannot be regarded as im p erm issib le p ra ctice . F romthe health point of view the ch oice is between carrying out the exam i­nation o r treatm en t fo r the sake o f the in d ivid u a l's health and notdoing so in o rd e r not to expose him to radiation. Obviously the d isadvantageis triflin g com p ared to that involved in not p erform in g ad iagn osis o r treatm en t.As far as the standards are con cern ed, all types o f m edical exposureare accordin gly excluded too, so as to prevent w orkers frombeing discrim in ated against and assigned to another job m e re ly b e ­cause they have undergone ra d iolog ica l exam ination o r radiotherapy.3.1.3. Concept o f maximum p erm issible doseIn defining the con cep t o f m axim um p e rm is s ib le d ose theICRP em phasizes that any m an-m ade radiation involves risk s. Hereare the very w ords used:"A ny departure from the environm ental conditions in which manhas evolved m ay entail a risk o f deleteriou s effects. It is th ereforeassum ed that long continued exposure to ionizing radiation additionalto that due to natural radiation background in volves som e r is k ." No66


This publication is no longer validPlease see http://www.ns-iaea.org/standards/radiation d ose in e x ce ss o f what resu lts from natural radiation canbe co n sid e re d as in n ocu ous. "H ow ev er, m an cannot en tirely d is ­pense with the use o f ionizing radiations, and th erefore the problemin p ractice is to lim it the radiation dose to that which involves a riskthat is not u nacceptable to the individual and to the population atla r g e . T his is ca lled a p e rm is s ib le dose."T h e re fo re "it is em p h asized that the m axim um p e rm is s ib led oses recom m en d ed are m axim um values; the C om m ission r e ­com m ends that all doses be kept as low as practicable, and that anyu nn ecessary exposure be a v oid ed ."Depending on whether the concept o f perm issib le dose is appliedto an individual o r to the population at la rg e , the em p h asis shouldbe put on the p reven tion o f som a tic o r o f gen etic e ffe c ts .3.1.4. C ategories o f p erson s exposedHuman bein gs lia b le to radiation ex p osu re a re cla s s ifie d intotwo c a te g o rie s :(1) In dividuals who a re o ccu p a tio n a lly e x p o sed to rad ia tion ;(2) Individual m em b ers o f the public (including p erson s livingin the v icin ity of con trolled a re a s).F o r each ca tegory , international organ iza tion s have sp ecifiedthe values of the maximum perm issible doses (these maximum valuesapply n eith er to exposu re due to natural backgrou nd radiation norto ex p osu re fo r m e d ica l p u rp o ses).3.2. BASIC STANDARDS3.2.1. GeneralT he b a s ic stan dards con stitute the c o r n e r -s to n e o f the w holesystem of regulations in the field o f ra d iologica l p rotection . Theyare supplem ented by p a rticu la r p ro v isio n s relatin g to the v a riou stypes o f ex p osu re, which constitute what m ay be ca lled d erivedstan d ard s.The first ca tegory o f p erson s exposed is what m ainly con cern su s. T hese a re w o rk e rs who are su bjected to reg u la r occu p ation alexposu re in the co u rse o f th eir w ork. A dm ittedly, it is d ifficu lt todeterm ine p r e c is e ly what is meant by 're g u la r1, yet it would be approp riate to give h ere a convenient adm inistrative cla ssifica tio n ofw ork ers, depending on the conditions o f w ork.67


This publication is no longer validPlease see http://www.ns-iaea.org/standards/A dm inistrative cla ssifica tio n o f w ork ersF o r ad m in istra tive p u rp oses it is convenient to c o n s id e r twocon ditions under w hich w o rk e rs are exposed to radiation in thecou rse o f th eir w ork. T his distinction depends on the p ossib ility ofa certain level o f dose being exceed ed , rather than the actual le v e lobserved, and w ill have an influence on arrangem ents for health su r­veillance and radiation protection as w ell as on the design and o p e r­ation of an installation.The two conditions are:(i) Conditions such that the resulting d oses might exceed threetenths of the annual maximum perm issible doses. This working con ­d ition sh all re q u ire that the w o rk e rs be su b ject to s p e c ia l healthsu pervision and person nel m onitoring. F o r these w ork ers the dosea sse ssm e n t w ill u su ally be a ch ieved by individual m on itorin g fo rexternal radiation o r internal contamination as appropriate, althoughthey may som etim es be made by indirect m ethods.(ii) Conditions such that the resulting d oses are m ost unlikelyto exceed three tenths o f the annual m axim um p e rm issib le d ose.W ork ers w orking under this condition would not requ ire individualm onitoring and special health supervision. F or these w orkers m onitorin g o f the w orking environm ent w ill u su ally be su fficien t, eventhough in som e ca ses individual m on itorin g m ay be d esira b le, e.g.to obtain statistical inform ation on the exp osu re.3.2.2. Standards applying to w orkers engaged in radiation w ork3. 2. 2. 1. E xposu re o f the whole body, gonads o r red bone m a rro wThe m axim um p e rm is s ib le d ose to the w hole body, gonads o rred bone m arrow of an individual shall be five rem s in any one year.A lso sin ce it is now estim ated that a w o rk e r should not r e c e iv e adose in e x ce ss o f 200 - 300 rem s fo r the whole span o f his w orkinglife , the follow in g form u la has been establish ed:D = 5(N- 18) remw here D is the d ose and N the w o r k e r 's age.6 8


This publication is no longer validPlease see http://www.ns-iaea.org/standards/E ighteen has been ch osen sin ce people do not n o rm a lly beginw orking b e fo re 18. T his form u la sets an upper lim it fo r the in d i­vid u al's accum ulated d ose at a given age. The radiation protectionstan dards m ake use o f th is fo rm u la to p rovid e fle x ib ility to m eetsom e p ra ctica l situations (these ca s e s , how ever, are felt to be in ­frequ en t). In such c a s e s , the total accum ulated d ose to the w holebody, gonads o r red bone m arrow of an individual shall not exceedthe maximum p erm issib le doses derived from the form ula. In otherw ords, the dose can exceed , if the form ula allow s, the yea rly lim ito f fiv e r e m s . H ow ever, the form u la m ight lead to a b u ses. F o rin stan ce, a w ork er starting at the age o f 50 yea rs - o r , in extrem eca ses, 58 years - would reckon 40 years of working life without anyexposu re. Consequently, if he had started work at 18 years old, hecould be exposed to 40 X 5 = 200 rem s and thus, without contradictingthe form ula, he could be subjected to 200 rem s during the first year,even during the first w eek. A s such a state o f a ffairs cannot beallow ed, the ru le establish ed by m eans o f the above form u la issupplem ented by another sp ecify in g that exp osu re shall in no ca seexceed three rem s in any con secu tive 13 w eeks. T his is an im ­portant lim itation as it m eans fo r instance that exposu re sh all notexceed 12 rem s in any one y ea r, whatever the w ork er's age and thetim e when he was first engaged in radiation w ork.S evera l s p e cia l p ro b le m s m ay a r is e when an in d ivid u a l'sp reviou s exp osu re is not known. In such a ca se the individual isassum ed to have receiv ed the m axim um dose; thus a person havingbeen engaged in radiation work at the age o f 28 years but whosep reviou s exposu re h istory is not known, w ill be con sid ered to havere ce iv e d a total d ose o f 50 re m s.T hese standards have varied with tim e. T here are people whohave been m onitored and have received higher exposu res than thosenow p erm itted. In this ca se, as the w ork er has been exp osed in am anner con form ing to previou s recom m endation s, no breach of theregulations is regarded as having o c c u r r e d . When new regulationsare brought into fo r c e , it is th erefore supposed that people have a c­cumulated the maxim um d ose.It should be noted, h ow ever, that in the ca se o f w om en o f r e ­productive capacity o r pregnant wom en sp ecia l p rov ision s are indicatedas w ill be m entioned la ter (see section 3. 2. 2. 8). A lso undersp e cia l conditions (see planned sp ecia l exp osu re, section 3. 2. 2. 3)an exp osu re o f up to 10 rem s fo r ca re fu lly scru tin ized individualsm ay be allow ed in one ex p osu re.6 9


This publication is no longer validPlease see http://www.ns-iaea.org/standards/3. 2. 2. 2. Partial exposureIn the case of partial exposu re, the first point to be con sideredis the exp osu re o f p a rticu la r organs due, fo r ex a m p le, to r a d io ­active contam ination. P a rtia l exp osu re being le s s se rio u s thanw h ole-b od y exposu re, an average value o f 15 rem s a y ear is p e r ­m itted with a m axim um value o f 8 rem s a qu a rter.F or three particular organs, the skin, thyroid and bone, a doseo f 30 rem s a year and 15 rem s a quarter is perm itted.F in a lly fo r e x tre m itie s - hands in p a rticu la r - the ex p osu rem ay be higher becau se o f the proxim ity o f the hands to the sou rce s,so a still higher value equal to 75 rem s a year and 40 rem s a quarteris perm itted.It should be em phasized that the y ea rly values a re the p rim a rylim its. The quarterly lim its fo r any organ can be up to half theyea rly lim it provided that the latter is not exceeded.Gonad exp osu re is included in w h ole-b od y e x p o su re . P a rtia lexposure involving gonad exposure must be regarded as w hole-bodyexposu re.A s fa r as the b o n e -m a rro w is co n ce rn e d , the ex p osu re m ustaffect it all. This is important in the case of a bone-seeking nuclideas it will irradiate the whole b on e-m arrow .3.2.2.3. Planned sp ecial exposureR adiation p rotection standards p rovid e s p e cia l gu idan ce fo rsituations which m ay o c c u r infrequently during n orm a l op era tion swhen it may be n ecessary to allow a few w orkers to receive exposurein e x ce s s o f the recom m en d ed qu a rterly lim it. In such c ir c u m ­stances, exposure o r intakes o f radioactive m aterial may be allowed,provided the dose com m itm ents do not exceed tw ice the annual doselim it in any sin g le even t and fiv e tim e s th is lim it in a life t im e .It is em phasized that doses o r intakes of this magnitude are onlyju stified when alternative techniques which do not involve such e x ­posures of w orkers are either unavailable o r im practicable.Planned s p e c ia l ex p osu re should not be allow ed u nder thefollow in g con d ition s:(a) If the addition of the intended dose to the w ork er's accum u­lated dose exceed s the amount determ ined by the form ula(b) If the w orker has received in the previous 12 months a singleexposure o r intake o f radioactive m aterial with a dose com m itm entin ex cess of the qu arterly quota70


This publication is no longer validPlease see http://www.ns-iaea.org/standards/(o) If the w orker has previou sly received an em ergency exposureo r intake o r an accidental exposure in excess o f five tim es the annualdose lim it(d) In the case of women of reproductive capacity.Doses resulting from planned special exposure shall be recordedwith those from usual exposures but any excess over the recom m endedlim its should not constitute a rea son fo r exclu din g a w o rk e r fromhis usual occu p a tion .3. 2. 2. 4. E m erg en cy exposu reEven during em ergen cy w ork, ev ery step w ill be taken to keepexposu re to a m inim um .D oses higher than those indicated in sections 3.2.2.1 and 3.2.2.2are acceptable when perform ing em ergen cy tasks during o r im m ediatelyafter an acciden t; they w ill be in cu rred only after com petentadvice has been obtained and w ill be co n sid e re d ju stified w h ere itis n e cessa ry to bring aid to individuals, to prevent the exposu re ofa large num ber o f person s o r to safeguard an im portant plant. It isnot p o ssib le to in dicate d ose lim its fo r such e x p o su re s, sin ce thea ccep tability o f the dose w ill depend on the im portan ce o f the p u r­p o se. In sofar as p o ssib le , w ork ers should be in form ed o f theh azards in volved b e fo re they a ccep t such e x p o su re s.If the dose exceed s tw ice the appropriate annual lim it (section s3.2.2.1 and 3.2.2.2), the situation w ill be exam ined by the com petentm ed ical authorities. The w orker m ay be authorized to continue withroutine work if there is no m ed ical ob jection and bearing in mind hisprevious exposu res, his health, age, special qualifications and socialand econom ic resp on sibilities.3. 2. 2. 5. E m ergency exposure to radioactive m aterialEven during em ergen cy w ork, every step w ill be taken to keepthe intake o f ra d ioactive substances to a m inim um .During em erg en cy exp osu re, it is im p ossib le to fo r e s e e thesca le of contam ination and it would th erefore be illo g ica l to indicatea lim it of intake. Such exposure w ill be con sid ered ju stified whereit is n e ce ssa ry to bring aid to individuals, to prevent the exposu reo f a la rg e num ber o f p e rso n s o r to safegu ard an im portant plant.Intake w ill be evaluated as fa r as p o s s ib le , and if it e x ce e d stw ice the annual lim it the situation w ill be examined by the competentauthorities . The w ork er m ay be authorized to continue with routine71


This publication is no longer validPlease see http://www.ns-iaea.org/standards/work if there is no m edical objection and bearing in mind his previouse x p o su re s, h is health, age, s p e cia l qu a lifica tion s and s o c ia l ande co n o m ic r e s p o n s ib ilitie s .3. 2. 2. 6. A ccid en ta l exposu reA ccidental exposure exceeding the lim its established for norm alw orking con ditions d iffe rs fro m e m e rg e n cy ex p osu re in that it isinevitable and u n foreseen . W orkers w ill be re fe rre d to the com p e­tent m ed ical authorities and d ecision s con cern in g any fu rth er w orkw ill be taken in the sam e way as provided in the ca se o f em ergen cyexposu re (section 3 . 2. 2. 4).3. 2. 2. 7. A ccidental intakesA cciden tal intake d iffers from em ergen cy intake only in that itis in evitable and u n foreseen . W ork ers w ill be r e fe r r e d to thecom petent m edical authorities and d ecision s con cern in g any furtherw ork w ill be taken in the sam e way as p rovid ed in the c a s e o f d e ­liberate em ergency exposure to radioactive m aterial (section 3.2.2.5).3. 2. 2. 8. Exposure of fem ale w orkersIn the ca se o f fem ale w ork ers regard m ust be had to potentialo r actual pregnancy and m axim um p e r m is s ib le d oses fo r w om eno f re p rod u cib le age and pregnant w om en m ust be esta b lish eda cco rd in g ly .W om en o f rep rod u ctiv e age should be assign ed job s w h ere e x ­p osu re o f the abdom en is lim ited to 1. 3 re m s o v e r a p e rio d o f 13w eek s, w hich c o rresp o n d s to 5 rem s a y e a r d e liv e re d at an evenrate. Under these con dition s, the d ose d eliv ered to the em b ry oduring the fir s t two m onths o f pregn ancy would n orm a lly be under1 rem , which is con sid e re d a ccep ta b le.When pregnancy has been diagnosed, steps must be taken to a s­certa in that the exposu re to which the w om an is su b jected is suchthat the average dose to the foetus during the rem ainder of pregnancyw ill not exceed 1 rem . In ca se s w here the d ose to the foetus m aybe alm ost equal to the d ose to the m oth er - fo r in stance when theabdom en is su b jected to penetrating radiation - th is req u irem en tis usually ensured if the m other is not subjected to dose rates higherthan 1.5 rem s a year.72


This publication is no longer validPlease see http://www.ns-iaea.org/standards/3. 2. 2. 9. Exposure of workers below .18 years of ageIn the case of a p erson whose occupational exposure begins b e ­lo w 18 y e a rs o f age, the d ose m u st not e x ce e d 5 re m s in any oney ear below 18 yea rs o f age, and the dose accum ulated by the age o f30 m ust not exceed 60 re m s. The ILO recom m ends that no w orkershall be engaged in radiation work below the age o f 16 which is alsoadopted by the IAEA.3.3. SECONDARY STANDARDS (DERIVED STANDARDS)3.3.1. GeneralIt w ill be r e c a lle d that the b a s ic stan dards a re e x p r e s s e d inrem s p er unit o f tim e . H ow ever, as d oses cannot be d ire ctlym ea su red in r e m s , the s o -c a lle d 's e c o n d a r y ' stan d ard s a reexpressed in practical units of m easurem ent, i.e. rontgens, particlefluxes and cu ries.The gen era l ru les lay down average valu es; con sequ ently thee x p o su re to w hich in dividuals o r grou p s o f in dividuals have b eensubjected can only be estim ated on the basis of m easurem ents eithero f the environment o r o f the individuals them selves.A ll the 's e co n d a ry stan dards' are a rriv ed at independently ofeach oth er, fo r one p a rticu la r type o f ex p osu re is co n sid e re d anda relationship is established between it and the b asic standards, a s­sum ing it to be the on ly type o f ex p osu re. T hus, to take the v e rysim ple case of X - o r gam m a-radiation, where the quality factor (QF)is equal to 1, an occupationally exposed w orker m ay not re ce iv e onthe average m ore than five rontgens a year, on the understanding thathe is not also exposed to neutrons o r radio nuclide sou rces.As far as radionuclides are con cern ed, a value is set fo r each,fo r exam ple the maximum p erm issib le body burden o r the maximump e r m is s ib le intake o r the m axim um p e r m is s ib le con cen tra tion inair. This value is established in such a way that the type of exposurew ill involve a m axim um exposu re of, fo r instance, 15 rem s a yearfo r a particular organ, assum ing the individual is not exposed to anyother external o r internal radiation.When all types o f exposu re are co n sid e re d , w eighting fa cto rsm ust be taken into account; in oth er w ord s, when se v e ra l hazardsare present at the sam e tim e, each contributes to the total exposure,which m ust not exceed the lim its laid down in the b a sic standards.73


This publication is no longer validPlease see http://www.ns-iaea.org/standards/The follow in g con sid eration s are th e re fo re v a lid / taking thevarious hazards into account sep arately. The secon d ary standardsare drawn up for the two main types o f irradiation , external ir r a d i­ation and radioa ctive contam ination. E xp osu res are e x p re ssed inrontgens w h ereas a b sorb ed d oses are e x p re ssed in rads and d oseequivalents are e x p re ssed in re m s.Maximum p erm issib le exposure means a single external exposurewhich, distributed in tim e and in sp ace through the body, d e liv e rsthe maximum p erm issib le dose to the individual. Maximum p e r ­m issible-con centration means a contamination such that the quantitieso f radionuclides present in the air and inhaled, o r present in drinkingw ater, leads to the m axim um p e rm issib le body burdens and thatthese m axim um p e rm issib le body burdens d eliver exactly the b a sicmaximum p erm issible dose. In practice, the maximum p erm issiblecon cen tration s fo r drinking water are not used in the health su p e r­v ision o f w ork ers..3. 3. 2. Secondary standards (derived lim its) foy external irradiationMaximum p erm issib le exposures are easy enough to define forexposure to electrom agn etic radiation (X and gamma rays). A ll thathas been said regarding the b asic standards can be applied d irectlyby replacing the rem unit by the rontgen unit. The resulting slighte r r o r o f 6% is quite accep table.Beta radiation is m ea su red in ion ization ch a m bers which areused for both beta and gamma radiation; and the m easurem ents canbe in terpreted in ra d s. The quality fa cto r (QF) fo r beta p a rticle sis assum ed to be equal to one. That being so the dose in rads c o r ­responds to the dose in rem s and the basic standards can be appliedd irectly to beta radiation by exp ressin g them in rads.T his cannot be done with neutrons; rem s m ust be con v ertedinto term s of maximum p erm issib le flux. In determ ining the m aximump e rm is s ib le neutron flux the follow in g co rre sp o n d e n ce isesta b lish ed .F o r th erm al neutrons with en erg ies of the o r d e r o f 0. <strong>025</strong> eV ,a flux of 670 n cm"2 s e c '1 is perm itted. The exposure resulting fromsuch a neutron flux is exactly equal to 5 rem s a year for w hole-bodyirra d ia tion . F o r partial ex p osu res corresp on d in g lim its m ust beapplied. The values given below co rresp on d to 5 rem s a y e a r fo ran occu p ation ally exposed w ork er.7 4


This publication is no longer validPlease see http://www.ns-iaea.org/standards/F o r neutrons other than therm al neutrons the p e rm issib le fluxwill vary in versely with the energy of the particles; thus for neutronso f 100 000 eV the perm itted flux falls to about one tenth o f 670, i.e.80 n cm '2 sec"1 . F or neutrons of 1 MeV the value is 18 n cm"2 sec"1and fo r neutrons above 3 M eV the value could fa ll fro m 18 to1.0 n cm -2 s e c -1 at 1000 MeV.When m easurem ents are made, it is found that it is not possiblein p ra ctice to establish the neutron spectru m to which a w ork er isexposed. F or this purpose threshold detectors are required, whichinvolves com p lica tion s. Consequently neutrons are usually dividedinto two o r m ore ca teg ories depending on th eir energy range.T herm al neutrons are m easured by m ethods which enable themto be m easured independently.F or fast neutrons, m easu red independently, the value adoptedis that which is m ost favourable from the point of.view of protection:all neutrons are assum ed to have the m axim um e n e rg ie s. The r e ­sulting e r r o r is on the safe sid e.3. 3. 3. 'Secondary standards' for radioactive contaminationThe corresp on d in g values fo r m axim um p e rm issib le con tam i­nations (e.g. m axim um p e rm issib le body burdens, m axim um p e r­m issib le con cen tration s, etc.) are m ore difficult to arriv e at. Theb a sic standards lay down that the average annual dose d eliv ered tothe whole body, the gonads and the red m a rrow should not exceed5 rem s. F or other organs, in a general manner, a value three tim esas high, i.e. 15 rem s a year, is allowed. F or the skin, where somesubstances such as arsenic get fixed, the thyroid, and bone the ICRPsp ecifies a lim it of 30 rem s a year.The following pages contain explanations with regard to determ i­nation of the m axim um p e rm issib le body burden and the m axim ump erm issib le con cen tration s. The only purpose o f including thisinform ation is to elucidate these con cep ts. In p ra ctice th ere is noneed to use the form u las given as the IC RP tables contain c o r r e s ­ponding values fo r all the m axim um p e rm issib le body burdens andcon cen tration s that have been calcu lated .3. 3. 3.1. M axim um p e rm issib le body burdensWhat m ust be determ ined then is the quantity o f ra d ion u clideswhich, permanently retained in the body at a given level, w ill deliver75


This publication is no longer validPlease see http://www.ns-iaea.org/standards/the pertinent lim iting dose - 5, 15 or 30 rem s a year - to the criticalorg a n . It is assu m ed that th ere is a state o f eq u ilibriu m and thatthe contamination is regular and continuous. Assum ing that w orkersare exposed throughout th eir working day, the daily doses in ex cesscounterbalance the daily doses beneath the maximum values.The maximum p erm issible body burdens (MPB) are given in theIC R P tables fo r approxim ately 250 d ifferen t ra d ion u clid es. T ocalculate these values one must know the radioactive ch a racteristicso f these radionuclides and th eir m etabolism . The ICRP has th e re ­fo re established the ch a ra cte ristics of a standard man on the basiso f b iolog ica l data. Thus his m u scle counts fo r 30 kg, skin 6. 1 kg,fat 10 kg, sk eleton 7 kg, red m a rrow 1 .5 kg, y ellow m a rro w1. 5 kg, e t c .The standard m an is estim ated to inhale 2X 107 cm 3 o f a ird a ily . During his 8 -h ou r w orking day he inhales as m uch a ir asduring the 16 h ours he is not at w ork . He is a lso a ssu m ed to a b ­s o r b 1. 2 litr e s o f w ater a day in liquid fo rm plus 1000 g o f w atercontained in his food, and water from oxidation p rocess is estimatedat 300 g; the total is th erefore 2 .5 litre s a day. The d ose is thendeterm ined as a function o f the body burden, as follow s:D. kqf E (QF)nmw here k is a unit con v ersion fa ctor; q is the radionuclide burden;f is the fraction o f radionuclide retained in the critica l organ (equalto 1 fo r the whole body); E is the energy d elivered by the p a rticles;QF is the quality fa ctor; n is a fa cto r o f n on -u n iform distribu tion(in som e ca se s radion u clid es a re not d istribu ted even ly with theresu lt that th ere is m ore exp osu re at one point than another); andm is the total m ass of the organ where the radionuclide is deposited.With this form ula the maximum p erm issib le body burden can becalculated, D being the maximum p erm issib le dose (5, 15 o r 30 rem sannually).. T his form u la can be applied to alm ost all radion u clidesexcep t th ose w hich behave in the bod y lik e .radium . Many humanob serv a tion s on radium are available fo r occu p ation ally exposedw ork ers, so it has been p ossib le to establish sep a ra tely the m a x i­mum p e rm issib le body burden fo r radium only.M axim um p e rm is s ib le body burdens fo r m a teria ls s im ila r toradium are calcu lated by m eans o f form u la (1), but substituting q'fo r q:p . kq’ fE' (Q F)n'm76


This publication is no longer validPlease see http://www.ns-iaea.org/standards/where f is the sam e since these are bon e-seekin g radionuclides; QFis the sam e sin ce they are alpha-em itters; and m is also unchangedsin ce it is the m ass of the bone system . Knowing that q' for radiumis equal to 0. 1 m ic r o c u r ie s , the differen t values o f the m axim ump e rm is s ib le body burden fo r su bstan ces s im ila r to radium can bed eriv ed .. It is thus p o ssib le to know the m axim um p e rm is s ib le bodyburdens fo r about 250 radion u clid es.E ach table o f m axim u m p e r m is s ib le body bu rdens re la te s tocontinuous exposu re under p articu lar con ditions, either 40 hours aweek; o r continuous exposu re fo r a week of 168 h ou rs.Though maximum p erm issible body burdens are of interest, theycannot solv e e v e ry p roblem as the burden o f radion u clides in ahuman body cannot be m easured d irectly, except for gam m a-em itters,w here sp e ctro m e te rs can be used fo r this pu rp ose, though withd ifficu lty.F or pure beta-em itters o r alpha-em itters recou rse must be hadto indirect m easurem ent o f intakes o r excreta.E xcretion m easu rem en ts are useful from the point o f view ofm onitoring person nel. T hey represen t a convenient m ethod, thoughit is difficu lt to deduce from a value fo r excreta activity m e a su re ­ment a value for the body contamination itself. The manner in whichradioactive substances are elim inated by the body is fa irly w ellknown. It also depends on the tim e that has elapsed sin ce the c o n ­tamination o ccu rred . Thus, from any given tim e when the body con ­tains a certa in quantity o f ra d ioa ctiv e su b sta n ces, e x cre tio n p r o ­ceeds according to a known law which is usually either an exponentialfunction, a pow er function o r a com bination of functions. In the caseo f acciden tal contam ination, from m easu rem en ts m ade at v ariou stim es it w ill be p ossib le to estim ate the amount present in the bodyat the tim e o f the acciden t.If, as is u su ally the ca s e , no in form ation is available on howthe contam ination o ccu rred o r the contam ination is irreg u la r, it b e­com e s exceed in g ly d ifficu lt to deduce in tern al con tam ination fro mm easurem ents made la ter. T h erefore, instead of trying to establishthe values fo r the m axim um p e rm is s ib le con cen tration in ex creta ,p referen ce has been given to establishing such values in inhaled o ringested substances. This has been done fo r air and drinking water,but not for food.In the fie ld o f in d u stria l h ygien e, con tam ination h aza rd s a rem ainly due to inhalation only. It is th erefore possible to solve som eproblem s of industrial hygiene by air m onitoring.77


This publication is no longer validPlease see http://www.ns-iaea.org/standards/As fa r as public hygiene is con cern ed, the contam ination of thepopulation at large o c c u r s m ainly through food , a little throughdrinking w ater, p ra ctica lly not at all by a ir.Owing to the com plexity of the problem no standards have beenlaid down for food. It would in fact be n ecessary to take into accountthe contribution each nuclide m akes to the total radionuclide intake,which w ill vary depending on the diet; and although m en all breathethe sam e way, they have not the sam e dietary habits.3. 3. 3. 2. M axim um p e rm issib le con cen tration sHow is it p o s s ib le to p ass fr o m m axim u m p e r m is s ib le bod yburdens to m axim um p e rm issib le con cen tration s in air and w ater?A num ber o f assum ptions a re m ade about the occu pation al activityo f w o rk e rs. The w ork in g sch edule a ccep ted fo r g en eral p u rp osesis 40 hours a week, divided into 5 days of 8 hours each and 50 weeksa year. E xposure is assum ed to be continuous. F rom these data arelationship can be established between m aximum p erm issib le bodyburdens and m axim um p erm issib le concentrations in air and w ater.The relation sh ip is sim p le enough. The m axim um p e r m is s ib lecon cen tration in air (M P C a) is given by the form u la(3)where k a is a unit con version factor; qf is the quantity of ra d ionuclidein the critic a l organ; T is the effectiv e h a lf-life ; fa is thefra ctio n o f inhaled ra d ion u clide w hich rea ch es the c r it ic a l organ ;and t is the p eriod o f e x p osu re.T h ere is a s im ila r form u la fo r the M PC value in w ater:qf(4)where fw is the fraction of ingested radionuclides which reach es thecritica l organ.Thus the M PC valu es a re lim itin g v alu es fo r the p ollu tion o fa ir o r drinking w ater corresp on d in g to the m axim um p e rm is s ib le7 8


This publication is no longer validPlease see http://www.ns-iaea.org/standards/d oses to the v a riou s organ s. T hey rep resen t average valu es o v e ra y ea r and m ay o cca sio n a lly be ex ceed ed .U nder th ese form u la s an in dividual cannot at any tim e in hislife be su b je ct, as a resu lt o f the in co rp o ra tio n o f ra d io n u clid e s,to an exposure o f the whole body o r a particu lar organ in e x ce ss ofthe b a sic standards laid down. T his does not m ean that the m a x i­mum p e rm issib le con cen tration o r body burden w ill alw ays involvean exposu re equal to the m axim um p e rm is s ib le d ose but on ly thatthe maximum p erm issible dose w ill never be exceeded. The follow ­ing exam ples w ill make the point cle a r.On a graph tim e t is plotted as an a b s c is s a and the d ose rateas the ord in ate. If we take a su bstan ce such as sod iu m -2 4 , eq u i­librium w ill be reached very quickly because the h a lf-life of sodiumis on ly a few h ou rs. Thus, applying the MPC form ulae (3) and (4),we find that an individual who from tim e z e ro inhales a ir con ta m i­nated with sodium in this con cen tra tion w ill r e c e iv e in his bod y asodium concentration which in creases slow ly so as to reach the lim itat a given tim e . A cu rv e o f the type show n in F ig .1 8 is ob ta in ed .DAYSFIG. 18. Internal contam ination due to exposure to sodium -2 4 .T he lim it w ill be rea ch ed , within 1%, at the beginning o f thefifth day. F o r a few d ays, until su ch tim e as the b od y bu rd en o fsodiu m re a ch e s eq u ilib riu m , the exposu re w ill be l e s s .A correspon din g curve w ill be obtained fo r io d in e -131 (F ig . 19);assuming that an individual starts work when 18 years old and is subjectedto continuous exposure to iodine, the lim it w ill be reached onthe fifty-third day.F o r ca lc iu m -45 the lim it w ill be p r a c tic a lly rea ch ed after1000 days, so that even though the m axim um p e r m is s ib le con ce n -79


This publication is no longer validPlease see http://www.ns-iaea.org/standards/tration in air is reach ed, this w ill during the first y ear involve theindividual in an exposu re le s s than the m axim um p erm issib le d ose.An e r r o r is th erefore m ade, but on the safe side (F ig . 19).1 10 100 1 000 10 000DAYSFIG. 19. Internal contam ination due to exposure to io d in e -131 and ca lciu m -4 5 .T his e r r o r on the con servativ e sid e b ecom es fa irly m arked inthe case o f elem ents with a v e ry long effectiv e h a lf-life such asstron tiu m -9 0 o r p lu ton iu m -239. F o r stron tiu m -90 the lim it isreached after 50 yea rs; if the w ork er starts w ork when he is 18 hew ill not have reach ed equ ilibriu m by the tim e he r e tire s and on ly thenw ill he have r e c e iv e d the m axim u m p e r m is s ib le d ose rate to thec r it ic a l org a n .F o r plutonium , w here the attainment o f equ ilibriu m is stillrem ote, it is on ly a fter 50 y ea rs o f w orking life that the m axim ump e rm issib le d ose (30 rem s a y ea r to bone) w ill be rea ch ed .Agreem ent has been reached on these standards, which are p e r­fe ctly valid and not difficu lt to put into p ra ctice; h ow ever, it m ustbe recogn ized that such calcu lation s approxim ate reality. Thus them axim um p erm issib le con cen tration s in air and w ater allow a doseto the body w hich fo r v e r y s h o r t-liv e d n u clid es is p r a c tic a lly them axim um p e rm issib le dose; fo r n uclides with a m edium h a lf-lifethe m axim um p e rm issib le d ose w ill be reach ed a fter a month o r ayear; while fo r v ery lo n g -liv e d nuclides the m axim um p erm issib led ose w ill never be reach ed.Instead o f con sid erin g that this m axim um p e rm issib le co n ce n ­tration should not be exceeded, the ICRP p roceed s on the basis thatn ever in an in d iv id u a l's life tim e should the in tegrated d ose beallowed to reach a value that might exceed the pertinent lim it. O bvi­80


This publication is no longer validPlease see http://www.ns-iaea.org/standards/ously, where one is dealing with a worker who has been subjectedfor 40 years, say, to plutonium or strontium contamination he will,by the end of his life, have received higher exposures than in youth.But workers do change jobs, and this is why for safety's sake it hasbeen deemed preferable that at no time should the concentration exceedthe value established, whatever the circumstances. In the case ofplutonium, however, the standards are particularly severe,especially during the first years at work. From the general pointof view of health protection, the method is perfectly valid since theresulting error, which is often considerable, is on the safe side.It is often difficult to apply the standards or to measure theconcentrations as very low levels are reached. This is a technicalproblem.3. 3. 3. 3. Use of the MPC tablesThese tables give the MPC values in air and water. The lateststandards relate to an exposure of either 40 hours a week or to acontinuous exposure of 168 hours a week.From these data it is possible to derive values for workers occupationallyexposed in actual conditions. Provision for this has beenmade because employment conditions vary from country to country.F or example for sim plicity's sake it has been agreed that the168 hour value, which may serve as a reference, must be multipliedby three to get the value for occupationally exposed workers witha working week of 40 to 48 hours, seeing that 168/3 = 56, and it isonly rarely that anyone will work as long as this. Accordingly avalue three times as high will be taken.The ICRP tables deal with 250 radionuclides; values given foreach radionuclide relate to the soluble and insoluble form as the casemay be; the values are also given separately for each critical organ.Owing to the fact that each radionuclide has its own metabolism,it is a relatively simple matter to apply the ICRP data in the eventof an isolated nuclide, but more difficult in the event of a mixtureof nuclides.In the case of known mixtures of nuclides the problem is simple:if they are all taken up by the same organ the values are added together.Thus, should a mixture of astatine and iodine deposit inthe thyroid, they are added together. The same is done for two boneseekingnuclides.81


This publication is no longer validPlease see http://www.ns-iaea.org/standards/In the event of intake of several radionuclides which are takenup by different organs, whole-body exposure must be consideredto have occurred, even though these organs are not the bloodformingorgans or gonads. In the first case the standard pertinentto the critical organ involved must be applied, and in the second case5 rems a year - the standard corresponding to the whole body -is used.If the nature of the radionuclide mixture is unknown, as is oftenthe case, the mixture is considered to be composed of the most toxicradionuclides. As this works out in an exceptionally severe manner,it is always desirable in practice to check on the presence or theabsence of a particular nuclide in an unknown mixture. The newtables give information on this point. Thus for a mixture in whichthere are no alpha-emitters, these being the most toxic, a lessstrict value is taken.The ICRP tables give typical examples where the most dangeroussubstances are eliminated one after another to arrive at the valuecorresponding to the most toxic nuclide the mixture can possiblycontain. In this way it is possible to get factors of 100, 1000 or even1 0 0 0 0; depending on the case.This procedure must be followed in every instance where airor water is contaminated by mixtures whose nature is not entirelyknown. It is always desirable to make a few qualitative analysesto prove certain highly toxic substances are not present or, if theyare. to determine them separately. Otherwise one must assumethat these substances make up the whole of the mixture, which maywell cause difficulty in applying the standards.Finally, when the nature of the mixture is known, the variouscontributions made by the different radionuclides must be taken intoaccount. The ICRP recommendations contain model formulas forsuch calculations.On a practical level this implies that the composition of themixture and the proportion of each radionuclide should be perfectlywell known. When an atmospheric analysis is being made, withfluctuations according to place and time, it will be essential to undertakeall necessary weighting calculations so as to determine themaximum permissible concentration, due account being taken of eachsubstance and the absence of any external irradiation being assumed.82


This publication is no longer validPlease see http://www.ns-iaea.org/standards/4. HEALTH SUPERVISION4. 1. RADIOLOGICAL MONITORINGAs stated earlier, the protection of workers against ionizingradiation requires both individual monitoring and medical examinations.The two types of supervision being complementary, in somecountries responsibility for both types of supervision is assumedby the medical service, in others it is divided between physicistsand physicians. When physicians are responsible for both individualmonitoring and medical examinations, their qualifications should,of course, extend to all the methods involved. When the physiciansare in charge of the medical examinations only, they should neverthelesstake account of the data obtained from physical monitoringin the interpretation of their findings.Therefore, as an aid to the physician, the methods of measuringexternal exposure or radioactive contamination to which personnelmay be subjected are described in this section of part 4.4. 1. 1. Methods of measurement of irradiation4. 1. 1.1. Measurement of external irradiation4. 1. 1. 1. 1. Measurement of electromagnetic (X, 7 ) radiation. Personnelmonitoring for electromagnetic ionizing radiation may bedone with films, pocket dosimeters, pocket ionization chambers orphotoluminescent or thermoluminescent dosimeters.Films (film badges) have a range varying according to the emulsionused, but no single emulsion can cover all requirements. Itis necessary sometimes to measure extremely low-level exposuresof the order of 10 to 1000 mR, and at other times doses of the orderof 1 to 1000 R. Detectors containing several emulsions may thereforebe used to record doses of interest for radiological protectionpurposes. The error of film badges is of the order of 20%, alwaysin the direction of a high reading, which constitutes a safety factor.The individual dose received may also be measured by meansof small ionization chambers. Some types are equipped withelectrometers and are known as pocket dosimeters (or pocketelectrom eters), while others are without electrom eters and aretermed pocket ionization chambers. The pocket dosimeters (pocketelectrometers) allow direct self-reading since the detector and the83


This publication is no longer validPlease see http://www.ns-iaea.org/standards/electrometer are connected. They are useful wherever it is of valueto have an immediate reading of the dose at any given moment.Pocket ionization chambers are intended for indirect reading,since the detector is separate from the electrom eter. They havethe advantage of being more economical but permit a reading of thedose only after a reasonably short time has elapsed. The range ofpocket dosimeters (pocket electrom eters) and pocket ionizationchambers is comparable to that of the film badge; in some casesthey are, however, more accurate.Film badges have the advantage over pocket dosimeters or ionizationchambers of leaving a permanent record for filing.Generally, film badges should be worn continuously by workersengaged in radiation work, while other dosimeters giving immediatereadings are useful when it is imperative to know the dose being receivedat any moment.New dosimeters are being developed, based on thermoluminescenceand photoluminescence phenomena. The types now availablecan give suitable information in the range of a few tens of m illirontgensto a few hundreds of rontgens.The steady development of these techniques points to an increasinguse of this type of detector in the future.4. 1. 1. 1. 2. Measurement of electron (beta) radiation. The monitoringapparatus described above used for gamma radiation mayalso be applied to the measurement of beta radiation. However, thewindows of the detectors must be sufficiently thin to allow passageof the beta particles to be measured. Beta particles of low energy,less than 0. 2 MeV for example, cannot be detected in currentpractice by means of personnel monitors. This is, however, nota serious disadvantage, since such low-energy beta irradiation cannotappreciably irradiate the human body from external sources.With regard to film badges, the same types can be used as forgamma-radiation monitoring. The wrapping is sufficiently thin toallow the beta radiation to pass. There are cases — those of mixedirradiation — when it may be desirable to distinguish between therespective contributions of beta particles and gamma rays, and itis then necessary only to place a light metal screen in front of apart of the film in order to shield the beta particles while allowingthe gamma radiation to pass. The difference in blackening betweenthe unshielded and the shielded areas gives an approximate indicationof the dose due to beta particles.84


This publication is no longer validPlease see http://www.ns-iaea.org/standards/Pocket electrometers and pocket ionization chambers normallyused for gamma rays can also serve as personnel monitors for betaradiation of energy greater than 0. 5 MeV. There are availabletypes of pocket electrometer and ionization chamber, with sufficientlythin walls of light material, capable of detecting beta radiation ofenergies as low as 0. 1 MeV.4. 1. 1. 1, 3. Measurement of neutron radiation. Although neutronsare not directly ionizing particles, they do produce nuclear reactionsin the matter through which they pass and the reactions in turn maygive rise to ionizing radiation capable of detection by the methodspreviously described. These nuclear reactions may also lead to theformation of induced radioisotopes, the radiation from which canlikewise be measured. It is thus possible to detect neutrons eitherduring or after irradiation.For the detection of neutrons during irradiation, monitoringapparatus of the types described above can be used, equipped withcertain accessories. Among these are cadmium scrieens able tocapture thermal neutrons and subsequently emit measurable' gammaradiation. Likewise, incorporation of b oron -10 in the detectorsmakes it possible to measure the alpha particles by the nuclearreactions between the neutrons and the boron.Highly energetic neutron radiation can be detected by photometricmethods using nuclear plates on which the number of tracksleft by recoil protons formed in a hydrogenated medium can be observedthrough a microscope.When the nuclear reactions induce radioactive substances, itis possible to determine the degree of neutron irradiation subsequently.One method consists in using in the detector, or gettingthe worker to carry on his person, certain metals which are rapidlyactivated by neutron radiation (e. g. indium, gold). In this way detectorswith several thresholds for neutrons of different energiescan be obtained. They can measure the neutron flux values for eachenergy range.In special circumstances it is even possible to use the humanbody as a monitor, since the sodium and phosphorus it contains areactivated by neutrons into the radioactive form s sodium -24 andphosphorus-32. By gamma spectrometry the amount of sodium-24contained in the whole body, the blood or the urine can then be determined.Similarly, the amount of phosphorus-32 contained in theblood or urine can be determined by beta radiochemical methods.85


This publication is no longer validPlease see http://www.ns-iaea.org/standards/4. 1. 1. 2. Measurement of radioactive contaminationRadioactive contamination is the second form of irradiation towhich workers handling radioactive materials may be subjected.Contamination may occur in various ways. It may be limited to thesurface of the body, in which case it is termed skin contamination,or radionuclides may penetrate into the body through the skin, digestivetract or lungs, when it constitutes internal contamination.It is therefore necessary to evaluate skin contamination on the onehand and internal contamination on the other. Evaluation of thelatter can be made either directly, as is possible in some cases,or indirectly, by measuring the amount of radioactive material liableto enter the body or the amount of such material eliminated fromthe body via the excreta.4. 1. 1. 2. 1. Measurement of external contamination. The evaluationof external contamination is relatively easy. The contaminated areashould first be demarcated by rough monitoring and a broad distinctionmade between the various possible contaminants. Knowledgeof the kind of work being performed usually provides an indicationof what has occurred. In any event it is easy, with the help of theavailable detectors, to make an immediate distinction between alphaemitters on the one hand and beta or gamma emitters on the other.The detectors used are generally proportional counters, Geiger-Miiller counters or scintillation counters. They are modified tosuit requirements and the detecting surface is usually flat for usein relatively open areas, or in the form of a probe for work in placesdifficult of access.The readings are expressed in counts per unit time. Accountmust first be taken of geometrical factors: the shape and surfacearea of the detector must be known in order to derive the number ofcounts per unit time and per unit area from the number per unittime. It is then necessary to take account of physical factors inorder to derive a value in curies per unit area from the number ofcounts. For this purpose the disintegration scheme of the radionuclides,together with the efficiency of the counter with regard tothe different types of radiation, must be known.Obviously, an exact determination of external contaminationis extremely laborious unless the nature of the contaminating nuclidesis previously known. External contamination is therefore frequentlyevaluated only in terms of alpha- or beta/gamma-emitting radio­86


This publication is no longer validPlease see http://www.ns-iaea.org/standards/nuclides. For this purpose maximum permissible limits have beenestablished irrespective of the nature of the contaminating radionuclide.Decontamination is regarded as necessary after accidentalcontamination above certain levels, the values of which, as establishedby a number of national organizations, are quoted in Appendix II tothe Manual on Safe Handling of Radioisotopes [15].4. 1. 1. 2. 2. Measurement of internal contamination. (1) Directmeasurement. In cases of internal contamination by radionuclides,it would appear theoretically highly advantageous to make an overallmeasurement of the contamination and thus to determine the bodyburden of radionuclides. Direct measurement is possible only ifthe radionuclides emit radiation capable of detection outside the body:at present this can be achieved, using spectrometry methods, onlyfor gamma-emitters. Various instruments may be used to makesuch measurements in vivo. Owing to their extreme sensitivity,they must be shielded most carefully from background radiation toensure accuracy of the results. For any given radionuclide thethreshold of detection depends on the effectiveness of the shielding.The materials most widely used for shielding such apparatus arewater, iron and lead. The types of apparatus used include ionizationchambers, liquid scintillators and crystal scintillators.The most frequently used apparatus is, however, the crystalgamma spectrometer. In its most usual form it consists of a detectingcrystal connected with a photomultiplier. The gamma raysemitted in the organism are absorbed by the crystal and producescintillations which in turn produce photoelectrons. The latter arethen amplified by the photomultiplier, and converted into electricpulses. These pulses are then transmitted to a single- or multichannelpulse-height analyser. With this equipment the radioactivityof the whole or of a particular part of the organism can be measured.An ionization chamber cannot achieve energy discriminationbetween gamma radiations, but this is to some extent possible ifliquid scintillators are used and is an easy task with crystal scintillators.In all cases the readings should be carefully interpreted,taking into account physical factors connected with the nature of thecontaminating radionuclides and geometrical factors connected withthe equipment. Calibration with regard to sources or phantoms isstill a delicate operation. However, the accuracy of the equipmentis generally sufficient to allow a correct evaluation of the bodyburden for certain radionuclides, such as iron-59, cobalt-60,zinc-65, ruthenium-106, iodine-131, caesium-137 and radium-226.87


This publication is no longer validPlease see http://www.ns-iaea.org/standards/Such apparatus is of value owing to the ease with which internalcontamination can be measured; it is particularly useful in caseswhere a workeris suspected of having undergone appreciable internalcontamination. It is not necessary to take samples, and care mustonly be taken to ensure that there is no interfering skin contamination.The characteristic features of the spectrometry method areits high sensitivity, adequate reliability and precision, great flexibilityand convenience of use. However, the equipment is expensiveat present and can only be used by experts.(2) Indirect measurement by monitoring of excreta. Since radioelementsare eliminated by excretion according to more or less wellknownlaws, it is possible to estimate from the quantity of nuclidesin the excreta the quantity present in the organism at a given time.The mode of elimination depends on the nature of the radio-element:uranium and plutonium are excreted in urine, strontium in sweatand urine. Radiochemical analyses are generally carried out onurine and occasionally on faeces and breath.Radiochemical techniques generally consist of the followingstages: preparation of samples; chemical isolation of radionuclides;quantitative determination of the latter by measurement of radioactivityafter calibration with a control sample; exact identificationof the radionuclides.The sampling of excreta in reality requires more care than atfirst appears, if it is to give a true picture of the degree of elim i­nation of the substance under consideration. The ideal procedureis to collect specimens over a period of 24 hours. However, inpractice, quantities equivalent to those excreted in 24 hours areoften used. This method is relatively easy for the sampling of urinebut not so easy for that of faeces. Specimens of both urine andfaeces are collected in flasks or Polythene bags, and a check mustbe made that there has been no excessive absorption of the radionuclideon the walls of the receptacle used for collection. Breathis collected in large balloons having inlet and exhaust valves. Thiskind of sampling can be carried out only in specialized laboratories.It is always useful to separate the various contaminating radionuclideswith a view to measuring the activity of each. Separationis effected by the physico-chemical methods of co-precipitation, adsorption,ion exchange, etc. .Quantitative determination of the radionuclides is effected bymeasuring the alpha, beta or gamma activity, using counters of the


This publication is no longer validPlease see http://www.ns-iaea.org/standards/G eiger-M uller, proportional or scintillation type, carefully calibratedby means of control samples. Special precautions shouldbe taken where there is a possibility of natural radioactivity (e. g.potassium-40) interfering with the artificial activity to be measuredin the specimens.Finally, steps must be taken to identify with absolute certaintythe radionuclide or nuclides to be detected. This operation iscarried out by the methods of chemical analysis, radioactive decay(if the half-life is sufficiently short, i. e. a few hours or days), absorption(for beta emitters), spectrometry (for alpha and gammaem itters) and tracks in nuclear emulsions (for alpha em itters).Special radiochem ical techniques have been developed to facilitatequantitative determination of radionuclides present in theexcreta, particularly the urine.The method adopted for this type of examination must meetcertain requirements: in particular it must be specific, sensitive,accurate and rapid. These conditions are, however, seldom fulfilledby any one technique.Often variants exist for different radionuclides. Methods whichare very highly sensitive but complex in application are used foroccasional but extremely important examinations (e. g. followingan accident). Other methods, less accurate and less sensitive buteasy to apply, are suitable for routine examinations. A list ofmethods of particular importance for medical toxicological analyseshas recently been prepared [16].In the great majority of cases, examinations are carried out onurine samples. The results can be used either to prove the existenceof even a very slight degree of internal contamination, correspondingto normal working conditions, or to determine the degree of internalcontamination following an accident. It may be supposed that eliminationtakes place according to a simple exponential law and thatcontamination has occurred in a regular manner and finally reachesa certain equilibrium. Given such conditions, the body burden ofan individual for a particular radionuclide may be determined fromthe radioactivity of the excreta. Such conditions are, of course,ideal; the nearest approach to them is in cases where radioactivematerials are absorbed in quantities that vary little from day to dayand are eliminated very slowly. On the basis of the fraction excretedper unit time, the total body burden of the organism may beestimated with some accuracy. In most cases, however, the nuclidesare eliminated in a manner which does not facilitate estimation of89


This publication is no longer validPlease see http://www.ns-iaea.org/standards/the total body burden. In such cases one can have warning concentrations,indicating that a small proportion of the maximum permissible body burden of radionuclides may have been retained inthe organism and that investigations should therefore continue, ordanger concentrations, indicating that a large proportion has beenretained and that urgent examinations and appropriate action areconsequently required. Interpretation of the results is easier incases of accidental contamination, in as much as the time and conditionsof the accident are generally fairly well known. It is usuallypossible, on the basis of several analyses made at definite times,to evaluate the initial body burden for the contaminating radionuclides.However, the difficulties of furnishing a sufficiently accurateestimate of the body burden on the basis of the quantities eliminatedin the excreta should always be borne in mind.(3) Indirect measurement by monitoring of environment. It is alsopossible to evaluate internal contamination indirectly from thequantity of radionuclides assumed to have entered the organism withincorporated substances (water, air, etc. ). The body burden r e ­sulting from ingestion or inhalation of radioactive substances contaminatingthe environment may be calculated by reference to thecontamination of the latter. This approach is particularly applicablein the case of atmospheric pollution, which is by far the mostimportant for purposes of industrial hygiene. Two methods of evaluationmay be used: the first is a rough method intended to givewarning, and the second, which is more precise, is applied in theevent of persistent contamination.The rough evaluation method consists of taking nasal swabs.Filter paper on holders is used for swabbing and is then unrolledfor monitoring of the alpha or beta/gamma activity. What is beingmeasured is in fact the easily removable part of the nasal contaminationand it is, of course, obvious that the results obtained arevitiated by a large number of errors. Moreover, numerous factors,such as the physico-chem ical form of the substances polluting theatmosphere, are disregarded.However, if considerable levels of activity are found on the nasalswabs, it may be inferred that appreciable radioactive contaminationhas occurred, but not necessarily that it has been converted intointernal contamination. A warning system of this kind makes itpossible for any toxicological or spectrometrical examinations thatare necessary to be undertaken at a later stage.9 0


This publication is no longer validPlease see http://www.ns-iaea.org/standards/A more precise evaluation of persistent internal contaminationcan be made quite indirectly from the results of environmental monitoring.If the atmospheric contamination at. any particular placeand time is known accurately, the quantity of radionuclides whichan individual worker has absorbed by inhalation can be deduced fromthese data. In practice an attempt is made, by judicious and fr e ­quent sampling, to obtain a fairly accurate picture of the atm osphereof the work place, a procedure which requires, great skill andcare. The method may be applied in uranium mines or radiochemicalplants. For every worker, the type of work done and the time spentover each operation must be known, and as representative data aspossible on the atmospheric pollution of the work place must be derivedfrom samples in flasks or on filters and from continuous recordingequipment. These data are weighted according to the typeand duration of the work done by the individual concerned. By determining,for an average individual, the quantities of air inhaledand the modes of absorption, the body burden at the end of a day,a week or a month may be deduced. These methods are undoubtedlycapable of offering excellent crosschecks in determining the bodyburden of radioactive substances which are difficult to measure directlyand slow in elimination, as is the case with alpha emitterssuch as radium or plutonium.4. 1. 2. Radiological monitoring organizationPersonnel monitoring should be carried out to determine thelevels of external irradiation and of radioactive contamination towhich the worker has been subjected. The methods described inearlier paragraphs are to be applied for this purpose.4. 1. 2. 1. Monitoring of external irradiation4.1. 2. 1. 1. Factors governing the organization of monitoring. Personnelmonitoring for external irradiation can and should be carriedout in a completely systematic manner, and the available methodsyield perfectly reliable data on the radiation doses to which personnelare exposed. However, the choice of method is governed by certainfactors, the principal of which are the following:(1) Spatial distribution. Irradiation of the body may be either wholeor partial, and among cases of whole-body irradiation some may bepractically homogeneous, such as exposure to gamma rays. In the91


This publication is no longer validPlease see http://www.ns-iaea.org/standards/case of neutron irradiation on the other hand, distribution in thebody is heterogeneous, depending on the orientation and energy ofthe neutron flux. With beta particles, the irradiation is limited tothe surface layers of the organism. However, in all cases of wholebodyexposure the monitoring apparatus is able to supply data fromwhich to estimate the resultant irradiation of the organism. In casesof partial exposure a distinction can be made between segmentarydeep irradiation by gamma rays or neutrons and segmentary superficialirradiation by beta particles. The demarcation of the partof the body irradiated is of great importance, but often it can be inferredonly from the circumstances of the exposure. It is also helpfulto have detectors judiciously placed in body regions particularlyliable to exposure, as for example the wrists, fingers and thorax.In most cases such a procedure makes it possible to determine segmentaryexposure, though certain instances of partial irradiationmay nevertheless pass undetected.(2) Time distribution. Besides its spatial distribution, the timedistribution of the dose is important. Therefore monitors have tobe used which yield data on both the intensity of the incident radiationand the amount of radiation received during a given period. The instrumentsfor measuring intensity are called dose-rate meters andthe most usual type is the portable ionization chamber, used forarea monitoring and warning purposes.(3) Types of radiation. The multiplicity of incident radiations alsopresents a problem for personnel monitoring and influences thechoice of method for measuring external irradiation. Externalirradiation is often due to mixed gamma and beta radiation, to whichneutron radiation must sometimes be added. Workers must thereforebe provided with dosimeters capable of recording these varioustypes of radiation. Personnel dosimeters at present available permitthis, and sometimes also furnish data on the energy of the incidentradiation.(4) Size of the dose. For monitoring under normal working conditions,the evaluation of small radiation doses of some tens or hundredsof millirems is called for, and dosimeters with a range extendingfrom 0 to 3 rem are fully adequate for this work. However,if there is an appreciable risk of accidental exposure, it is essentialfor workers to be equipped also with dosimeters capable of recording92


This publication is no longer validPlease see http://www.ns-iaea.org/standards/doses up to 1 0 0 0 rem at least, otherwise after an accident greatdifficulty may arise in evaluating the doses actually received. Suchdosimeters are com m ercially available and it is, in fact, alreadypossible to obtain dosimeters capable of meeting the requirementsof both routine and emergency monitoring.4. 1. 2. 1. 2. Organization of monitoring in practice. (1) Whole-bodyexposure. Personnel dosimeters yield adequate data. They shouldbe worn continuously and the exposure checked at appropriate intervals.Measurement of total beta/gamma and neutron activity shouldbe systematically performed and the results should also distinguishbetween the gamma, beta and neutron fractions. Doses expressedin rontgen units or in terms of particle flux should be converted intorem Units to indicate accumulation. Film dosimeters can be developedat intervals of from onie to thirteen weeks, depending on thenature of the hazard and on administrative conditions. The currentpractice is to carry out weekly readings, but there is no objectionto making them on a monthly or quarterly basis only, since thesereadings in fact indicate only the dose accumulated during a relativelyshort period, a week or a month for example. All doses are enteredin the external exposure record of each worker and added togetherso as to give the accumulated dose-time curve. From thiscurve it can be decided whether the exposures received are com ­patible with the maximum permissible dose formula recommendedby the <strong>International</strong> Commission on Radiological Protection.(2) Partial exposure. The above data on whole-body exposure shouldbe supplemented by information on partial exposures. For this purposemonitors should be worn in the region of the hands or thefingers whenever a predominant exposure of the extremities may,occur.In the same way, for ionizing radiation leading chiefly to skinexposure (beta), detectors may usefully be worn which give a separaterecord of doses due to penetrating radiation (X, gamma) andto soft radiation (beta). The results are recorded separately.(3) Accidental exposure. When the work carried on entails a ccidentalexposure hazards (nuclear reactors, particle accelerators),detectors should be worn which can measure high doses of the orderof several tens or hundreds of rems. ,93


This publication is no longer validPlease see http://www.ns-iaea.org/standards/As a matter of fact, detectors used under normal conditionsare usually saturated by such high doses. Therefore, detectors forelectromagnetic, electron and neutron radiation must be used, witha range of sensitivity corresponding to these potential high exposures.4. 1. 2. 2. Monitoring of radioactive contamination4. 1. 2. 2. 1. Factors governing the organization of monitoring. Themeasurement of the radioactive contamination of an individual stillremains one of the most difficult problems in the field of radiologicalprotection. While it is relatively easy to evaluate skin contamination,it is a very tricky matter to estimate internal contaminationby either direct or indirect methods. In addition, the methods usedcall for highly specialized equipment and personnel. Therefore onlyoccasional individual monitoring for radioactive contamination canbe regarded as a practical possibility. It should be twofold innature:on the one hand, any normal work with unsealed radioactive sourcesshould be accompanied by periodical measurements of external orinternal contamination, the results of which should be compared withthose obtained from area monitoring at the work place; on the otherhand, individual monitoring should be carried out whenever an incidentor an accident involving the risk'of radioactive contaminationhas occurred. The results then provide a final answer to the questionto what extent, if any, contamination has affected the workerspresent.(1) Spatial distribution. As with external irradiation, it is importantin any case of radioactive contamination to know the spatial distributionof the dose. This can be determined very easily for skin contamination,but the spatial distribution of internal contamination isgoverned by the physico-chem ical properties and the metabolismof the radionuclide. Acquaintance with the nature of the contaminatingnuclide is therefore a prerequisite for determining the degreeof irradiation of the different organs of the body.(2) Time distribution. Various factors affect the time distributionof the dose. These include the physico-chemical form in which thecontaminating substance occurs and the radioactive properties, particularlythe half-life, of the radionuclides. Thus, in the case ofskin contamination, a distinction must be made between the initial94


This publication is no longer validPlease see http://www.ns-iaea.org/standards/contamination and the residual contamination after treatment. Inthat of internal contamination, the radioactive substances move inthe organism in accordance with their metabolism. The biologicalhalf-life may be defined as the time necessary for half the radionuclideto be eliminated from a given organ or from the wholeorganism. The contaminating nuclides have also a radioactive halflifewhich is the time necessary for half their atoms to decay. Itis the combination of these two half-lives which represents the timenecessary for the radioactivity in the organ or organism concernedto fall to half its original amount; this is termed the effective halflife.It is therefore logical that particular attention should be devotedto evaluating contamination by radioactive substances whichbecome fixed in the organism for a considerable length of time andhave a long radioactive half-life. Irradiation extending over severalyears or even over the life-time of the individual may indeed occur,as is the case with the most toxic radionuclides, such as strontium,plutonium, radium, etc.(3) Nature of radionuclide. Sometimes the contamination is dueto one radionuclide only, but it is very often multiple. A correctappraisal of the degree of irradiation of the organism and an accuratededuction of the probable consequences are possible only if the natureof the contaminating radionuclides is known. In dealing with skincontamination this is less important and it is often thought sufficientto estimate the contamination in term s of alpha and beta/gammaemitting substances. This simplified procedure can also be adoptedwith internal contamination, but here there is every advantage tobe gained from determining the respective contribution of each ofthe contaminating nuclides.(4) Extent of contamination. From the foregoing remarks it willbe apparent that the measurement of radioactive contamination re ­mains an extremely intractable problem. The interpretation ofreadings depends on a number of arbitrary hypotheses regardingthe geometrical conditions, in the case of direct measurement ofinternal contamination, and regarding the basic laws of metabolism,in the case of indirect measurement from the excreta. Moreover,the radioactivity levels to be detected under normal working conditionsare extremely low; while it is relatively easy to detect accidentalcontamination, it is very difficult to evaluate correctly regularcontamination lower than the maximum permissible body burdensin the organism.95


This publication is no longer validPlease see http://www.ns-iaea.org/standards/Recently the ICRP has issued a report where the problem ofdose evaluation from internally deposited radionuclides is discussed,to which the reader is referred for more detailed information [17].4. 1. 2. 2. 2. Organization of monitoring in practice. (1) Externalcontamination. As regards skin contamination, the work is relativelyeasy and the detectors already described can be used for evaluatingcontamination by both alpha and beta/gamma emitters. The fr e ­quency of this monitoring should be governed by the extent of thecontamination hazard. Wherever unsealed radioactive sources liableto produce an appreciable amount of surface contamination are handled,monitoring should be carried out daily or even twice daily, aftereach half-day's work. Workers should normally wash before beingmonitored in order to safeguard the monitoring instruments fromcontamination, and the measurement made is therefore of residualcontamination after washing. When normal washing procedures areineffective in removing the contamination, and decontamination undermedical supervision has been resorted to, the exposure readingsobtained must be entered in the records. Maximum perm issiblelevels have not been definitively established by the <strong>International</strong>Commission on Radiological Protection; however, the tables appearingin Appendix II to the IAEA Manual [15] may be referred to as anindication.(2) Internal contamination. For internal contamination, monitoringshould be carried out periodically, the frequency again dependingon the extent of the hazard. Thus, for work with radionuclides usedas tracers, annual monitoring is sufficient, while for operationsinvolving substantial quantities of radioactivity twice-yearly, quarterlyor even more frequent surveys should be undertaken. As hasalready been seen, various direct or indirect methods may be used.Gamma spectrometry makes it possible to carry out periodic surveysfairly easily so as to evaluate the body burden of gamma-emittingnuclides. It should, however, be noted that this is a rather expensivemethod. Radiochemical analyses of the excreta, particularlythe urine, are therefore preferred.A knowledge of the radionuclides with which the given individualis working makes it possible to determine the kind of examinationrequired. However, these examinations need only be made at presentin respect of persons exposed to considerable internal contaminationhazards. In certain cases, as has been described above,96


This publication is no longer validPlease see http://www.ns-iaea.org/standards/it is possible to determine the quantities of radionuclides likely tohave been inhaled on the basis of the contamination of the atmosphereand the conditions of work. All these readings for internal contaminationof the worker should permit the calculation of total annualfigures, indicating the dose received by the organism as a wholeand by particular organs. Obviously this can be done only if thenumber of contaminating radionuclides and the contribution of eachto the dose is known.(3) Accidental exposure. Any incident or accident where appreciableradioactive contamination is suspected or has occurred must befollowed by monitoring. If gamma emitters are concerned, gammaspectrometryprovides an easy and quick means of evaluating thebody burden. If alpha or beta emitters are concerned, radiochemicalanalyses of blood and excreta (particularly urine) will make itpossible to estimate the body burden. This estimate can be madeon the basis of a study of the contamination of blood, urine and faecesas a function of time. In any case interpretation proves rather difficult,however, with regard to the mathematical models chosen forradionuclide elimination (usually an exponential function or lessoften a power function).4. 1. 3. Estimation of the absorbed dose4. 1. 3. 1. Summation of exposuresThe preceding paragraphs contain a description of methods ofevaluating irradiation, both from external radiation and radioactivecontamination. It is no easy matter to add together the dose valuesdue to the various types of irradiation, but an attempt to do so shouldbe made whenever practicable, though there is a great differencebetween the readings for external irradiation and those for radio -active contamination. It is relatively easy, with the help of continuouslyoperating dosim eters, to obtain approximate estimatesof the total exposure dose due to external radiation. Data on radioactivecontamination on the other hand, are highly unsatisfactoryand indicate only the body burden of radionuclides at a given moment.In theory, therefore, considerable interpretation work is neededin connection with internal irradiation, although in practice suchwork is undertaken only if the exposure exceeds about 1 0 % of theperm issible concentration. Be that as it may, the various expo­97


This publication is no longer validPlease see http://www.ns-iaea.org/standards/sures should be added together as far as possible and the resultsexpressed in units valid for all types of irradiation. These unitsare the unit of absorbed dose, the rad and — when account is takenof the Quality Factor — the rem. It will therefore be necessaryto convert to rems results obtained in rontgens or curies or in termsof particle flux.4. 1. 3. 2. Spatial distribution of the doseBesides the problems involved in merely adding together thedifferent types of irradiation, there are those of obtaining satisfactorydata on the spatial distribution of the dose. These lattercan be obtained only by precise identification of the radiation andthe radionuclides. This is unavoidable as the maximum permissibledoses recommended by the <strong>International</strong> Commission on RadiologicalProtection have been established differently for whole-body exposureand for partial exposure affecting the skin or different organs.In practice, therefore, all types of radiation likely to result in arelatively homogeneous distribution of the dose within the body willbe added together. . Thus, the doses due to gamma and neutron radiationand to radionuclides considered as diffusing uniformly inthe organism (sodium, potassium,tritium, etc. )will together formone total. Separate totals will have to be made for the irradiationof particular organs. To take as an example one of the most im ­portant cases, that of the bone, it will be necessary to addtogether all the doses received by incorporation of bone -seeking radionuclides, such as radium, plutonium, strontium,etc. , and by irradiation of the skeleton from generally diffused radionuclides(sodium, potassium, tritium, etc. ). It is thus possibleto determine the doses actually received by the most important o r­gans - skeleton, thyroid, skin, digestive tract, lungs, etc. Separatetotals should also be obtained for exposure of the extremities,especially the hands, comprising the overall exposure of the bodyplus the particular additional exposure of the members in question.This concept of spatial distribution of the dose therefore leads usto consider different kinds of exposure, either of the organism asa whole or of some part of it. Although it might appear advantageousto evaluate the total absorbed dose, this is in reality oflimited importance, as no maximum permissible level has yet beenestablished for the integral dose delivered to the whole body.98


This publication is no longer validPlease see http://www.ns-iaea.org/standards/4. 1. 3. 3. Time distribution of the doseIt is fully acceptable for dose readings to be taken at intervalsof some weeks or months since the period quoted by the ICRP is13 weeks. Measurements covering shorter periods are of valueonly for administrative purposes. As mentioned above, it is relativelyeasy to obtain adequate information on the circumstances ofan external exposure. The wearing of direct-reading dosimetersand the use of personal or portable dose-rate meters often makeit possible to evaluate how exposure has fluctuated in the courseof time. The procedure is more complex in the case of radioactivecontamination and it is often difficult to deduce the dose receivedover a period from a given degree of radioactive contamination. Thehypothesis normally adopted is that there is an exponential decreaseof the dose in time; this is expressed in term s of effective halflife.It will thus be seen that the precise determination of the timedistribution of the absorbed dose is not simple.4. 1. 3.4. Influence of the type of radiation and radionuclideIn addition to the spatial and time distribution of the absorbeddose, the type of radiation also has its part to play in the origin ofradiobiological effects. It is therefore necessary to use the QualityFactors (QF) for alpha, beta, gamma and neutron radiations; onlythus it is possible to determine the sum of the doses in rem s. Itmust not be forgotten, however, that the QF depends on a very largenumber of variables besides the type of radiation, including thecircumstances of exposure, the nature of the effects produced, etc.4. 1. 3. 5. Practical conclusionIn fact, all the above procedures can provide is a tentative evaluationbecause, although relatively accurate data are obtainableon total or partial external exposure, it is a very difficult matterto obtain precise figures on internal contamination of the organismas a whole or of a particular organ. Therefore, when the level ofinternal contamination is not too high, it is usually thought sufficientto try and obtain exact data regarding external irradiation exposureand no more than summary indications concerning internal radioactivecontamination. However, in cases where considerable radioactivecontamination has occurred, or where the hazards associated99


This publication is no longer validPlease see http://www.ns-iaea.org/standards/with the work are sufficiently great, the utmost should be done toestablish such total doses, since they alone make possible a fullevaluation of the risks incurred by a worker through exposure. Asradiochemical analysis and spectrometry methods develop, progressivelybetter results may be expected.4.2. MEDICAL SUPERVISION4.2. 1. Responsibility of the medical serviceThe medical service is responsible for the medical aspects ofradiological protection. It is responsible for selecting personnelfor work involving actual or potential exposure to ionizing radiation(pre-employment medical examination), holding medical examinationsduring employment and, in particular, carrying out special examinationsand laboratory tests for persons exposed at or above maximumpermissible levels and undertaking the diagnosis and treatmentof radiation injury in cases of accident.Finally, an additional reason for medical surveillance is to demonstrateover a long period the normality of the incidence ofdisease in groups of people exposed to radiation within the permissiblelimits.The ICRP gives general guidance as to what the aim of healthsurveillance is. The ICRP indicates that the assessment of healthbefore and during employment is directed towards determiningwhether the health of the worker is compatible with the tasks forwhich he is employed. The type and extent of the surveillance shouldbe essentially the same as in general industrial medical practice andshould include both pre-employment and routine examinations, thefrequency of the latter being determined mainly by the individual'sgeneral health and the conditions of the work. Workers where exposuremay exceed 3/10 of the maximum perm issible doses (seesection 3. 2. 1) may require more detailed surveillance to providea background of information which could be useful in the event ofa serious over-exposure, and to detect any conditions contraindicatingemployment or specific tasks. Provision should also bemade for any necessary tasks and examinations on individuals whohave received abnormal exposure referred to the medical officer.The ICRP qualifies abnormal exposure as being exposure receivedby a worker which exceeds the maximum perm issible doses re -100


This publication is no longer validPlease see http://www.ns-iaea.org/standards/commended for normal practice. Such exposures can be either voluntary,in which case they are called.em ergency exposures, orinvoluntary, when they are termed accidental exposures.Medical officers should therefore be acquainted with the dutiesof workers, with the working environment and with the radiologicalhazards to which the latter may be exposed. They should ascertainthat levels of exposure are in accordance with the standards andregulations in force and should keep, or at least have access to, allrecords of workers' overall exposure and radioactive contamination.In addition, they should carry out general and special medical examinationsin order to detect any disorder or illness which might bedue to ionizing radiation. With the aid of up-to-date health records,they can compare the results of these examinations with the resultsof personnel monitoring, with a view to establishing causal relationshipswhenever pathological disturbances appear.In cases of accident, the responsible medical officer must takethe necessary decisions. If there are no detectable clinical symptomsand the total irradiation of the body is less than 3 rem s, a simplewarning is sufficient. If the total irradiation due to an accidentalexposure or due to an intake of radioactive material exceeds twicethe annual limit, the ICRP states that "the situation should be reviewedby a competent medical authority. The worker may still beallowed to continue routine work if there is no objection from themedical standpoint, due account having been taken of his previousexposure, health, age and special skills, as well as his social andeconomic responsibilities". Having taken these various factors intoconsideration, if detectable clinical symptoms are found, the necessarysteps must betaken to permit the individual to spend theperiod necessary for recovery outside the range of any radiationsource, either by transfer to another post or by temporary or permanentsuspension from work. In addition the medical officer mustapply first aid and other treatment appropriate to the case.The medical service should have accurate knowledge of the radiologicalhazards to which workers are subjected. It should takepart in the planning of safety measures taken to limit workers' exposureto permissible levels and should be acquainted with all thedata concerning the radiological environment in which the workersare placed.The medical service should take part in giving workers inserviceinstruction on radiological protection. This consists mainlyin an educational task. Workers must be properly informed of the101


This publication is no longer validPlease see http://www.ns-iaea.org/standards/radiological hazards linked to their job assignment. In some cases,they may be trained in using the necessary preventive devices.Finally, they must be instructed in the usefulness of the variousmeans of radiological detection and methods of medical examination.The duties of the medical service can be adequately fulfilledonly provided extremely close collaboration is established with theservice responsible for physical monitoring of radiation. The medicalservice should indicate the general rules to be observed andrequest that the necessary physical surveys be carried out. It shouldbe provided with all personnel monitoring data and should also begiven such information about the general working conditions as willenable it to determine the extent to which work places are subjectto exposure and contamination. The closest liaison must also beestablished between the medical service and the management of theestablishment.In general, the activities of the medical service should be r e ­garded as confidential, concerning as they do data of a personal nature.This confidential character must, however, in no way beallowed to impede the improvement of working conditions. The importanceof health records, standardized in such a manner as to permittheir use for statistical purposes, should consequently be stressed.Furthermore, the confidential character of the activities of themedical service should not have the effect of obstructing the exchangeof information on the irradiation to which workers have been subjectedor on their state of health. In particular, if a worker changeshis employment, all relevant data must be passed on. The dose formularecommended by the ICRP applies throughout a worker's working life.The fact also that the latent period between the exposure and its pathologicaleffects may extend over several years requires that medicalrecords be preserved for an adequate period after cessation of employment,and that the medical service have access to them.4. 2. 2. Medical examinationAs suggested above, radiation workers should undergo medicalexaminations before, during and, preferably, after employment.These examinations do not differ basically from those carried outin industrial medicine, but reflect certain specific requirementsresulting from the special nature of the work done by the workersin question.102


This publication is no longer validPlease see http://www.ns-iaea.org/standards/4. 2. 2. 1. Medical historyEvery medical examination should begin with a thorough inquiryregarding the family, personal and occupational history ofthe worker.4.2.'2. 1.1. Family history. Family history is of importance becausegenetic disturbances are a significant part of the possibleeffects of irradiation. Particular attention should therefore be givento any history of hereditary, family and congenital diseases, andit is also useful to know the incidence of cancer and leukaemias. Theinvestigations should relate to ascendants (parents and grandparents),collaterals (brothers, sisters and cousins), descendants (children)and also the spouse and his or her direct ascendants.4. 2. 2. 1. 2. Personal history. Accurate data on the w orker's personalhistory are important, facilitating as they do an evaluationof his state of health before employment. Care should be taken toinvestigate all disorders which may have affected organs or organicfunctions that are particularly radiosensitive or liable to damageas a result of work with radiation. The investigations should thereforebe made to bear on haematological diseases (anaemia, granulopenia,haemorrhagic disthesis), skin diseases (dermatitis, dermatoses),diseases of the digestive tract (acute or chronic), diseasesof the lungs (infectious or allergic) and diseases of the eyes (cataract,conjunctivitis).4. 2. 2. 1. 3. Occupational history. Finally, the w orker's occupationalhistory should be carefully noted. Injuries at work and previousoccupational diseases should be recorded. However, the historyof any work done with radiation or with radiomimetic toxic preparationspresents the greatest interest, and any occupation involvingradiation exposure and, in particular, any cases of over-exposureor radioactive contamination should therefore be faithfully recorded.Previous work with benzol, other hydrocarbons and all other carcinogensor mutagens must also be.carefully noted.4. 2. 2. 2. Examinations4. 2. 2. 2. 1. General examinations. General examinations shouldbe such as to give a proper picture of the worker's state of health. A103


This publication is no longer validPlease see http://www.ns-iaea.org/standards/detailed description of such examinations is unnecessary here sincethe investigations usually made in good industrial medical practiceshould be sufficient. Thus, anthropometrical data (weight, height,morphology) and the results of examination of the main organs andfunctions (cardiovascular system, digestive system, respiratorysystem, nervous system and endocrine glands, blood and haematopoieticorgans, liver and kidneys, locomotor system, skin and senseorgans, genital system) should be recorded.These examinations should be supplemented by radiologicalexaminations and biochemical tests of certain characteristics of theblood and urine. The fact that the workers in question are exposedto irradiation hazards is no reason for neglecting to make the necessaryradiological examinations (lungs and other).In the medical care of radiation workers, it is of course themost radiosensitive organs and their functional or haematologicalcondition which present the greatest interest. It will therefore benecessary to give particular attention to the blood and bone marrow,the skin, lungs, digestive tract, sense organs and genital system.4. 2. 2 . 2. 2. Haematological examinations. It should be rememberedthat the sensitivity of ordinary haematological methods of examinationis grossly insufficient for the detection of radiation effectsat levels at or slightly above maximum permissible levels. However,the purpose of these examinations is on the one hand to provide ageneral picture and on the other to detect the smallest anomaliesof the blood that might possibly be due to irradiation. Investigationsshould cover both the peripheral blood and the blood-formingorgans, but for all regular inspections before or during employmentit is recommended that examination be confined to the peripheralblood only. Examination of the blood-forming organs proper shouldbe considered only in cases of over-exposure or considerable radioactivecontamination.Examinations of the peripheral blood include , not only bloodcounts but also the study of morphological or functional changesin the blood cells. The blood count should give the number per cubicmillimetre of erythrocytes, reticulocytes, total leucocytes, granulocytes,(neutrophils, basophils, acidophils, [ eosinophils]), lymphocytes,monocytes and thrombocytes. In addition, Arneth's formulaefor granulocytes are recommended. However, in calculating theeffect of radiation on numerical changes in the white blood count,account must be taken of the fact that the day-to-day variation of an104


This publication is no longer validPlease see http://www.ns-iaea.org/standards/individual's white blood count is about 15% and the technical errorin an average case is estimated at 1 0 % even with carefully standardizedtechniques. Changes in blood count only become manifest withrelatively high doses, and consequently cannot be used as a sensitivetest to evaluate the effects of moderate or low-level irradiation.Attention should also be given therefore to morphological changessuch as anisocytosis and poikilocytosis in erythrocytes, abnormalcytoplasmic granulation in granulocytes, bi-lobed nuclei and chromophilegranulation in lymphocytes, and changes of size or structurein thrombocytes. A careful watch should also be kept for immatureform s of the red or white series. These examinations should besupplemented by tests of the functional capacity of the circulating,blood. It is necessary to determine the haemoglobin concentration,haematocrit reading and blood-coagulation factors, and to makethrombo-elastrography. These haematological examinations shouldbe made before employment and at sufficiently regular intervalsduring employment to make it possible to follow trends in a givenhaematological condition. However, some of these examinations,especially those regarding morphological changes, can only becarried out in research laboratories and are not indicated as routinemeasures.In cases of over-exposure, it may be necessary to perform asternal puncture, so as to obtain a myelogram, including both countand formula. This test is of particular interest if a prognosis hasto be made, or therapeutical indications given for an over-exposedworker. Occasionally, and much more rarely, adenograms maybe made in addition.4. 2. 2. 2. 3. Cytological examinations. Great interest is now shownin the fundamental cytological changes which can be related to exposure.These are mainly the concern of chromosomal examinations,but such studies, on blood cells in particular, present serious difficultiesfrom the practical point of view as well as in regard to interpretation.Therefore, in our present state of knowledge theyshould be considered only in cases of over-exposure following anaccident.4. 2. 2. 2.4. Examination of the skin. Dermatological examinationsare of value in that they provide information on the state of an organwhich, generally speaking, is sensitive to radiation and, moreover,runs the greatest risk of exposure. In all cases of exposure to soft105


This publication is no longer validPlease see http://www.ns-iaea.org/standards/radiation, such as beta particles, the skin in fact absorbs almostthe entire amount. Also, in handling radioactive substances, theskin of the hands is exclusively or at least primarily exposed. Itis therefore advisable to make a survey of the condition of the skin,especially with a view to detecting the chronic dermatoses whichincrease its radiosensitivity. In addition, examination should bemade of the hands and fingers in order to evaluate the functional ormorphological changes possibly occurring as a result of chronicirradiation. Some authorities have accordingly recommended —though their advice has been little heeded — the regular taking offingerprints as a means of observing progressive deterioration ofthe contour of the skin and detecting affection of the epidermis asshown by flattening. A study of the capillary circulation also providesvaluable data on subjacent affection of the dermis and conjunctivetissue. Finally, a precise tactile examination may usefullysupplement the two previous examinations.4. 2. 2. 2. 5. Examination of the eyes. The eye is generally regardedas a critical organ. Though the lens is sensitive to X- and gammarays, it is particularly sensitive to external radiation composed ofrelatively heavy particles, such as neutrons, protons, etc.4. 2. 2. 2. 6 . Examination of the mouth, ear, nose and throat. Whereworkers are exposed to the risk of radioactive contamination, inparticular by pollution of the atmosphere, the upper respiratory anddigestive tracts are the first to be contaminated. Radioactive particlesmay remain for some period in contact with the mucous membranesof the mouth, the nose and the pharyngo-laryngeal region.This may lead to local irradiation and disorders of the epitheliumwhich can be detected by regular examination. Therefore a mouthand ear-nose-throat inspection should be made periodically, andan immediate examination effected in case of an accident involvingsignificant radioactive contamination.4. 2. 2. 2. 7. Examinations of the lungs. Examination of the lung isgenerally carried out on a regular basis in industrial medicine, inview of the high incidence of diseases of the respiratory system.Such examinations are particularly necessary whenever work is donein a polluted-atmosphere and they should therefore be carried outon persons engaged in work involving risk of contamination fromthat source. The information sought should indicate the morpho­106


This publication is no longer validPlease see http://www.ns-iaea.org/standards/logical and functional condition of the lungs; particular attentionshould be devoted to detecting conditions of fibrosis, chronic bronchitisor of emphysema, and the vital capacity and other lungfunctions should be tested. Special importance attaches to radiologicalexamination of the lungs as a check on the w orker's health.4. 2. 2. 2. 8. Examination of ^the digestive tract. The digestive tractis recognized as one of the critical organs, as it is often heavilyirradiated during inhalation or ingestion of radioactive substances.It should, however, be recognized that, unlike the preceding case,the digestive tract does not lend itself readily to examinations likelyto reveal small changes in its structure or functions.4. 2. 2. 2. 9. Examination of the liver and kidneys. The importantrole played by the liver and kidneys as organs of excretion in generaland of elimination of radioactive substances in particular iswell known. It is therefore useful to have information on the functionalstatus of these organs in a case of regular or accidental radioactivecontamination. Liver and kidney, however, cannot be expectedto reveal the effects of even a significant degree of irradiation,as their radiosensitivity is too low as compared with that of otherorgans.4. 2. 2. 2. 10. Examination of the genital system. The study of thegonads has a double significance — both genetic and somatic. Thegenetic effects of irradiation can of course only be evaluated in thedescendants, but in the somatic field it is possible to point to immediateconsequences. The spermatogenic function is extremely radiosensitivein the male, so much so that its study is a particularlyvaluable test for evaluating the radiation dose absorbed. However,for various reasons, such examinations cannot be carried out systematically.They should, however, be made in all cases of significantover-exposure, when a count of the spermatozoa and a studyof their morphological and functional changes are called for. Particularattention should be paid to the detection of abnormal forms,abnormal nuclei, caudal bifidity and motility disturbances, and alsoincreased fragility.In the female, on the other hand, the effects of irradiation aremuch more difficult to detect and disturbances of the menstrual cyclebecome evident only at very high doses.In woman too, the progress of any pregnancy should be followedattentively from the time it is known or reported.1 07


This publication is no longer validPlease see http://www.ns-iaea.org/standards/4. 2. 2. 2. 11. Neurological and psychiatric examination. The effectsof radiation on the nervous system at relatively low levels aremainly functional. Low-level irradiations may, according to someauthors, lead to certain disturbances, the transitory nature of which,however, makes the practical application of functional tests im ­possible. In the case of whole-body exposure, nevertheless it maybe of value to study the electroencephalogram for neurologicalchanges.Neuro-psychiatric examinations are also very useful in assessingthe suitability of workers for responsible posts where human deficiencycould have serious results (reactor or accelerator operation).4. 2. 2. 2. 12. Biochemical examination. The purpose of biochemicalexamination is to study general or particular changes of metabolism,especially those more or less specifically connected with ir ­radiation. The determination of the main characteristics of theblood or urine is of relatively secondary interest, except as regardsurea excretion and for very high radiation doses. On the other hand,the urinary excretion of amino acids is highly important, any significantirradiation being followed by an increase of aminoaciduria,and it is recommended that the nature and quantity of excreted aminoacids be determined by chromatographic analysis. In cases of overexposureadditional amino acids appear and the quantities eliminatedincrease significantly. For certain amino acids, such as aminoisobutyricacid and taurine, the quantities eliminated are to someextent proportionally related to the dose received and determinationof them is, therefore, of some value. The normal aminoacidexcretion rate should therefore be determined for every workerliable to significant over-exposure and the actual excretion ratechecked regularly. Since aminoaciduria can be a constitutional abnormality,it is not possible to draw any precise conclusions fromaminoaciduria discovered following an over-exposure unless thepreceding levels of amino-acid excretion are known.Enzymological and other biochemical examinations may alsobe performed on the blood but they still belong to the field of r e ­search. Immuno-electrophoretic examination of the plasma, onthe other hand, may have real value in cases of over-exposure.4. 2. 3. Organization of medical supervisionMedical supervision should be organized in such a way as tomake it possible, in the case of each worker, to assess beforehand108


This publication is no longer validPlease see http://www.ns-iaea.org/standards/his suitability for the type of work to which it is proposed to assignhim, to keep a regular record of this health during employment and,subsequently, to intervene in the event of any late occupationaldisease.4. 2. 3. 1. Pre-employment supervisionBefore any worker liable to exposure to radiation is engaged,a report should be established to serve two purposes; firstly, toserve as a basis for determining to what extent the past history andthe present condition of the worker make it possible to regard himas fit or unfit for the type of work for which he is being considered;and secondly, if he proves fit for such work, to serve as a referencepoint for any subsequent changes due to the hazards of thatwork. Every worker should therefore undergo a pre-employmentinquiry and medical examination.4. 2. 3. 1. 1. Medical history. As explained above, the inquiry hasthe purpose of determining the candidate's hereditary, personal andoccupational history. It is of particular importance that all previousirradiations be noted, for which purpose an account shouldbe kept of external exposures and an attempt made to obtain as muchdata as possible on any radioactive contamination. A gammaspectrometricalexamination may be useful for evaluating as appropriatethe present body burden of gamma-emitting nuclides. In theanalysis of previous exposures, a.distinction should be made betweenthose due to work with radiation and those due to radiological examinationor treatment. The former must be taken into account later,during employment, for the assignment of maximum perm issiblecumulative limits. The latter, however, should be ignored whendetermining the accumulated dose, although they should still be carefullynoted. In some cases, especially after extensive radiotherapy,an additional occupational exposure might seem inadvisable. Onlythe medical officer, however, is qualified to determine to what extentsuch previous therapeutic irradiations are compatible with subsequentwork involving radiation hazards taking into account the environmentof work as well. Any possibility of previous poisoningby radiomimetic substances must also be recorded. Although itis difficult to establish a precise relationship between the effect ofradiomimetic substances and that of radiation, there is no doubt thatprevious poisoning, especially by hydrocarbons, may be a factor1 0 9


This publication is no longer validPlease see http://www.ns-iaea.org/standards/in not allowing a worker to engage in work connected with radiation.In this respect again, each case must be considered individually andit is for the medical officer to decide to what extent disturbancesdue to chemical radiomimetic agents may contra-indicate subsequentwork involving exposure to radiation.4. 2. 3. 1. 2. Medical examination. Taking into consideration theadministrative classification of workers (cf. section 3.2.1), com ­plete medical examination should be carried out, preferably notmore than two months before engagement, and should comprise, asexplained above, a general examination comparable to those madein industrial medicine and special examinations of the most radiosensitiveorgans. The former indicate the candidate's general fitnessfor employment, and the latter aim at determining to whatextent he is fit for the special work, involving a risk of externalirradiation or radioactive contamination, upon which he is to be engaged.The special examinations should therefore be specificallyadapted to the kind of work for which the candidate is intended. Thefollowing remarks may be taken as an indication. If there is to bea risk of significant whole-body exposure or general contamination,a haematological examination should be made. If there is a likelihoodof exposure to soft (beta) radiation, of skin contamination (alphaand beta emitters) or of actually handling radioactive substances,a dermatological survey should be made, supplemented by a carefulexamination of the hands and fingers. The risk of atmosphericpollution by radioactive substances is extremely high if unsealedsources are handled and in this case, particularly if pollution byradioactive dust is involved, an examination of the lungs must alwaysbe carried out to reveal any morphological changes and tocheck the functioning of the respiratory system. If the work involvesexposure to neutron radiation or heavy particles, the condition ofthe lens should be determined by ophthalmological examination. Itis therefore necessary for the medical officer to have at his disposalan occupational hazard record, as described below.4. 2. 3. 1. 3. Decision regarding fitness for work. The medical historyand the general and special medical examinations should yieldconclusions regarding the candidate's fitness for a given type ofwork. Candidates are classified on the basis of a number of c r i­teria, the choice of which is an extremely complex matter. Definitestandards for judging a candidate's fitness are highly desirable, but110


This publication is no longer validPlease see http://www.ns-iaea.org/standards/as yet no such standards exist. Blood-count values are those thathave been most generally fixed, but they vary from country tocountry depending on geographical, physiological and biological conditionsand on the techniques used.Summing up, it must be borne in mind that each case has tobe considered individually and that the medical officer, and he alone,is responsible for determining whether the man is fit for a particularjob. Poisoning by radiomimetic substances or excessive therapeuticirradiation may give the medical officer grounds for hesitation r e ­garding an individual's fitness. As far as medical examinationsare concerned, it is impossible to define quantitatively the limitsbeyond which skin disorders, morphological or functional changesof the lungs, slight abnormalities of the lens, etc. should contraindicatework involving the risk of skin contamination, atmosphericpollution or neutron irradiation respectively.In all cases decisions must be based on both the medical historyas a whole and the results of the medical examinations. Candidatesare, as a rule, classified in three categories: individualsplaced in the first category are considered fit for work involvingthe risk of external exposure or radioactive contamination; thosein the second are considered temporarily unfit for such work; can-. didates in the third category are declared permanently unfit. Personsplaced in the second category should remain under medical observationfor a certain period, during which further examinations arecarried out to determine whether an improvement in their conditionrenders them fit for the employment intended. It should bestressed that a final decision. of unfitness should only be taken afterseveral confirmatory examinations. Conclusions and decisions shouldbe recorded in the worker's medical file, as described below.4.2. 3. 2. Supervision during employment4. 2 .3.2. 1. General. During employment, medical examinationsshould be carried out at regular intervals. Exposure or contaminationmay in fact sometimes easily remain unnoticed and, consequently,efforts must be made to detect any effects. On the otherhand, changes in an individual1s state of health may occur whichmay seem to be due to ionizing radiation, but are in reality due toother causes. Even so, they provide a reason for taking the individualoff any work involving considerable exposure and contaminationhazards. All these factors therefore point to the advisability of re­111


This publication is no longer validPlease see http://www.ns-iaea.org/standards/gular medical examinations during employment, their nature andfrequency depending, of course, on the occupational hazardsinvolved.4. 2. 3. 2. 2, Nature of the examinations. It has been explained inpreceding paragraphs that these examinations should comprise generalinvestigations supplemented by special examinations of theorgans likely to be most affected by external exposure or radioactivecontamination.In usual practice, a number of examinations have to be madefor all workers submitted to ionizing radiation. These are generalclinical examinations. Others should be performed only when theradiological hazards so require. The following cases may be mentionedas examples.In case of whole-body exposure to penetrating radiation or contaminationof the organism by radionuclides that are distributed generally,haematological examinations are recommended becauseall the blood-form ing tissues will have been irradiated.In the event of external exposure to radiation with a high linearenergy transfer (LET), especially in the case of irradiation of thehead, ophthalmological examinations should be undertaken to keepthe state of the lens under regular review.In the event of contamination by radioactive dust, as in uraniummines or certain workshops where radioactive substances arehandled in powder form , examination of the lungs is essential todetermine the condition of the pulmonary tissues.In the event of contamination by kidney-seeking radionuclidesor radionuclides with a toxic effect on the kidneys, the morphologicaland functional condition of these organs should be kept underregular review.4. 2. 3. 2. 3. Frequency of examinations. The frequency of theseexaminations will naturally vary. In many countries the minimumis one examination per year. The optimum frequency depends ontwo factors. Firstly, the occupational hazards have to be taken intoaccount, as regards both their nature and their extent. In this respect,the occupational hazard sheets referred to below play anessential role. The extent of the hazards may be judged from theresults of area monitoring of radiation and from the level of radioactivecontamination at the work-place. Secondly, the frequency ofexamination should be governed by the state of health of the worker112


This publication is no longer validPlease see http://www.ns-iaea.org/standards/concerned. In the case of workers in whom a particular organ showsmorphological change or signs of functional disorder, the examinationsshould, of course, be carried out at more frequent intervals.4. 2. 3. 2.4. Abnormal exposure and special examinations. Workersmay be exposed under certain circumstances to doses higher thanthe MPD recommended for normal practice. In an emergency exposurethe exposure is voluntary, while in an accidental exposureit is involuntary. The <strong>International</strong> Commission on RadiologicalProtection visualizes that in either condition it is unrealistic torecommended dose limits. The ICRP and the IAEA Basic <strong>Safety</strong>Standards for Radiation Protection [14] also indicate that the dosesreceived in abnormal circumstances should be recorded togetherand.be clearly distinguished from normal exposures. If the doseor intake of radioactive material exceeds twice the annual limit, thesituation should be reviewed by a competent medical authority, dueaccount having been taken 'of the person's previous exposures, health,age and special skills as well as his special and economic responsibilities.It must therefore be emphasized that the magnitude ofthe dose received by an individual and the implied risk contributeonly one, although an important element to the assessment of thecircumstances which would determine whether a worker should continuehis radiation work, if he has been subject to an exposure inexcess of the appropriate maximum permissible doses. To be ableto assess the w orker's fitness for further work, examinations,additional to the foregoing which are appropriate for normal workingconditions, may be necessary. In the event of an abnormal exposure,special examinations must obviously be carried out to detect anydisturbances and find out as far as possible whether there are anycorrelations between the accidental irradiation or contamination andthe clinical symptoms.Whereas such far-reaching investigations as myelogram studies,chromosome or lymphocyte abnormalities and tests of liver andkidney function are not appropriate in normal circumstances, theymay be very valuable in the event of radiation accidents.4. 2. 3. 3. Medical examination at termination of employment andpost-employment follow-upAll workers who have worked under condition i (see section3. 2. 1, administrative classification of workers) should undergo a113


This publication is no longer validPlease see http://www.ns-iaea.org/standards/medical examination by a suitably qualified physician at or shortlyafter the termination of their employment. Depending on the resultsof this examination, it may be necessary to provide further followupcare after employment has ceased.The follow-up care would not of course include monitoringexcept possibly in cases of significant body burdens of radionuclides.It is generally desirable that it should include some type of medicalexamination intended to detect late effects of ionizing radiation.4.3. HEALTH FILES4.3. 1. GeneralWell-organized supervision of workers exposed to ionizing radiationis inconceivable without systematic and accurate records ofall the data yielded by physical monitoring and medical examinations.The data in question are, of course, those relating to the individualworker himself. Consequently, readings obtained from environmentalmonitoring (environmental radiation, contamination of airand water) should not be recorded, but all data on exposure of theindividual (film badge and electrometer readings, skin contamination,internal contamination) should be included in the worker1s file togetherwith the results of the medical examinations undergone.These data constitute individual health files which must be kept underconditions of medical secrecy as defined by the competent authoritiesin each country.The health file consists of: job assignment and occupational hazardsheets, from which can be inferred, in respect of each worker, theworking conditions to be established and the radiation and contaminationhazards to which he may be exposed; radiation and medicalfiles containing ali data yielded by physical monitoring and medicalexamination before, during and after employment; and, preferably,a separate register of occupational accidents or diseases. All abnormalexposures should be recorded together and clearly distinguishedfrom normal exposure.4. 3. 2. Job assignment and occupational hazard sheets4. 3. 2.1. Job assignment sheetEach w orker's file should contain a record of the posts heldby him, and it is therefore useful to introduce what may be termed114


This publication is no longer validPlease see http://www.ns-iaea.org/standards/a job assignment sheet. This document is started when the workeris recruited for the first post held and should indicate all changes ofpost. Such information is basic and if it is desired to determinea worker's contamination level by the indirect method of calculatingfrom the pollution level or each work place, the time spent at eachjob must also be indicated. From the administrative point of viewthis may entail a considerable amount of work and a com prom isesolution must sometimes be adopted. However, it is the only re ­latively accurate means of evaluating internal contamination by deductionfrom the working conditions.4. 3. 2. 2. Occupational hazard sheetThe job assignment sheet should be supplemented by an occupationalhazard sheet providing information on the hazards of externalexposure or radioactive contamination involved in each operation.These records should be kept with great accuracy, as theyrepresent the only possibility of establishing a causal relationshipbetween occupational activity, radiation levels and the w orker'sstate of health. The occupational hazard sheets should be suitablyamended whenever the working conditions change.4.3.3. Radiation and medical files4. 3. 3.1. Radiation filesRadiation files should include all available evidence for evaluatingw orker's radiation exposure or contamination.Before actual recruitment, the radiation files should includedata on previous occupational exposure and, as appropriate, on otherconsiderable non-occupational irradiation or exposure to radiomimeticsubstances, together with a statement of the level of internalcontamination where this is thought to be advisable.The principal entries to be made in the file during employmentare a record of the physical monitoring results. They should berecorded in such a way as first, to facilitate summation of the dosesreceived from external exposure and radioactive contamination, andso make it possible to determine the dose accumulated after threemonths, six months or a year; and, secondly, to enable one to determineat any moment, by means of a graph, whether the dose receivedin the course of the preceding quarter has remained within115


This publication is no longer validPlease see http://www.ns-iaea.org/standards/the maximum permissible level (3 rems in the case of a whole-bodyirradiation).After cessation of employment, the file should present a recordof the exposure and contamination to which the worker has been subjectedduring employment.The doses received from external exposure or radioactive contaminationshould be added together year by year and a grand totalfound wherever appropriate. As mentioned previously, all abnormalexposures should be recorded together and be clearly distinguishedfrom normal exposures.4. 3. 3. 2. Medical filesThe medical file should include all available data on the w orker'sstate of health. Before actual recruitment, the file should includethe results of the inquiry and pre-employment medical examinationto determine fitness for work involving radiological hazards.During employment, the file should contain an account of theworker's medical supervision, particularly the special examinations.Only significant and positive facts revealed by the examinationshould, of course, be recorded. Comparison of this set of data withthe radiation file will be made with a view to establishing possiblecausal relationships between any health disorders and occupationalexposure. It may be pointed out that for most radiopathologicaleffects where a threshold exists, it is possible to establish such acausal relationship; for example, skin disorders can be easily relatedto radiation exposures of known level. For individual cases,however, it is impossible to establish a causal relationship betweena disturbance where a threshold does not exist and a given exposure;thus one cannot, in an individual case, relate with certainty anoccurrence of leukaemia to previous exposures.On cessation of employment, the file should contain a sheet indicatingthe w orker's health record. A summary of the resultsof the medical examinations, both general and special, should alsobe included. Special mention must be made of any abnormalitiesthat may be related to occupational exposure. Finally, an indicationshould be given of the w orker's state of health on cessation ofemployment.If a worker is transferred to another establishment, it may beof value to prepare an employment termination sheet containing abrief summary of the preceding data for the use of the medical serviceof the new establishment.116


This publication is no longer validPlease see http://www.ns-iaea.org/standards/4.3.4. R ecord in g o f occupational a ccid en ts and d isea ses4. 3.4. 1. Occupational accidentsAny accidents which have occurred in the course of work shouldbe recorded. All doses received in abnormal exposures (i.e.duringemergency situations or as a result of a radiation accident) shouldbe recorded together and clearly distinguished from normal exposures.It is often useful to include in accident records both the physicalmonitoring data and the findings of medical examinations. In particular,all medical examinations made following an accident, togetherwith their results and the decisions taken, should be mentioned.4. 3. 4. 2. Occupational diseasesThe health file must contain mention of any occupational diseasesthat may occur. These may be assumed occupational diseases, i. e.those that may be due to ionizing radiation but for which no causalrelationship has been established, especially if working conditionscomply with the standards laid down by the <strong>International</strong> Commissionon Radiological Protection.In cases of true occupational disease, related to abnormal workingconditions, both the medical findings with regard to the diseaseand the results of physical monitoring with regard to the exposureconditions should be recorded.4.3.5. NotificationThe individual files contain information on each worker1s radiationexposures and state of health. Workers asking for them maybe given the results recorded in their individual files. The 1confidential'notification of radiological data is recorded individuallyby name in case of over-exposure. The ' non-confidential' notificationof radiological data can be collective and anonymous only;it may be of interest in cases of normal exposure complying withthe radiation protection standards.117


This publication is no longer validPlease see http://www.ns-iaea.org/standards/REFERENCES[1] KINSMAN, S ., Radiological Health Handbook, US Department o f Health, Washington, D .C .(1954).[2] KUZIN, A .M ., SHAPIRO, U .I ., Osnovy radiacionnoj biologii, Moscow (1964).[3] INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Report No. 10a, PergamonPress, Oxford.[4] LANGHAM, W .H ., BRODES, P .M ., GRAHN, D ., Radiation biology and space environmentalparameters in manned spacecraft design and operations. Aerospace Med. 36 2 (1965) S ec.II,1-55.[5] CLAUS, W .D ., E d ., Radiation Biology and M edicine, Addison-W esley, Reading, Mass.(1958).[6 ] UNITED NATIONS, General Assembly, XVII Session, 1962, Suppl. 16, UNSCEAR Rep.[7] UPTON, A .C ., The dose-response relation in radiation-induced cancer. Cancer Res. 21(1961) 717. ~[8] UNITED NATIONS, General Assem bly, XIX Session, 1964, Suppl. 14, UNSCEAR Rep.[9] LINDELL, B ., DOBSON, R. L . , Ionizing Radiation and Health, WHO, G eneva (1961).[10] UNITED NATIONS, General Assem bly. XIII Session, 1958, Suppl. 17, UNSCEAR Rep.[11] INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Rep. Com m ittee II onPermissible Dose for Internal Radiations, Pergamon Press, New York (1959).[12] SLOUKA, V ., Ziklady toxikologie radioaktivnfch IStek, Prague (1962).[13] INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION. Report N o.9, PergamonPress, Oxford (1966).[14] INTERNATIONAL ATOMIC ENERGY AGENCY, Basic <strong>Safety</strong> Standards for Radiation Protection,1967 Edition, <strong>Safety</strong> <strong>Series</strong> N o.9, IAEA, Vienna (1967).[15] INTERNATIONAL ATOMIC ENERGY AGENCY, Safe Handling o f Radioisotopes (First Editionwith Revised Appendix I), <strong>Safety</strong> <strong>Series</strong> N o .l, IAEA, Vienna (1962),[16] WORLD HEALTH ORGANIZATION, Methods o f Radiochemical Analysis, WHO, Geneva (1966).[17] INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Evaluation o fRadiation Doses to Body Tissues from Internal Contamination Due to Occupational Exposure,Publication N o.10, Pergamon Press, Oxford.BIBLIOGRAPHYNATIONAL BUREAU OF STANDARDS, Radiobiological Dosimetry, Handbook 88, NBS, Washington,D .C . (1963).RAJEWSKY, B ., Ed., Wissenschaftliche Grundlagen des Strahlenschutzes, G. Braun, Karlsruhe (1957).SACQ, Z .M ., ALEXANDER, P .A ., Fundamentals o f Radiobiology, Pergamon Press, Oxford (1961).WORLD HEALTH ORGANIZATION, Effects o f Radiation on Human Heredity, T echnical Reports<strong>Series</strong> No. 166, WHO, Geneva (1959).WORLD HEALTH ORGANIZATION, Radiation Hazards in Perspective, Tech nical Reports <strong>Series</strong>N o .248, WHO, Geneva (1962).WORLD HEALTH ORGANIZATION, Public Health and the M edical Use o f Ionizing Radiation,Technical Reports <strong>Series</strong> N o .306, WHO, Geneva (1965).WORLD HEALTH ORGANIZATION, Planning o f Radiotherapy Facilities, Technical Repons <strong>Series</strong>N o.328, WHO. Geneva (1966).WORLD HEALTH ORGANIZATION, M edical Supervision o f Radiation W ork, T ech nical Reports<strong>Series</strong> No. 196, WHO, Geneva (1960).118


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This publication is no longer validPlease see http://www.ns-iaea.org/standards/INTERNATIONALATOMIC ENERGY AGENCYVIENNA, <strong>1968</strong>SUBJECT GROUP: IINuclear <strong>Safety</strong> and Environmental Protection/Radiological <strong>Safety</strong>PRICE: Austrian Schillings 124,—

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